UI24PC320CS · OOP THROUGH JAVA · UNIT I · LAB 0 · AFTER CLASS 4 EXACTLY

Everything is taught.
Now you type.

Four classes gave you println, Scanner, data types, arrays and every operator, branch and loop. Lab 0 asks for nothing new — it asks for your fingers. Four small programs at home before lab day, three exercises in the lab. Seven programs, one folder, two hours.

TIME BUDGET2 hours in the lab · 20–25 min prelab at home

PROGRAMS7 total — 4 prelab at home + 3 on lab day

MARKS100 — rubric on the last page, read it first

PREREQUISITEClasses 1–4 — every mechanic already taught

STEP 0 · BEFORE ANY CODE — MAKE THE FOLDER, SO EVERY FILE HAS A HOME

EVERY FILE IN THIS LAB IS SAVED HERE — NO EXCEPTIONS C:\Users\<you>\Desktop\java-practice\lab-00\

COMMAND PROMPT — MAKE THE FOLDER FIRST, BEFORE ANY CODE

C:\Users\diya> cd Desktop\java-practice

C:\Users\diya\Desktop\java-practice> mkdir lab-00

C:\Users\diya\Desktop\java-practice> cd lab-00

C:\Users\diya\Desktop\java-practice\lab-00> _

That last prompt is your working directory — every javac and java in this lab runs from exactly here. If your prompt doesn't end in lab-00, stop and cd until it does. ✦

Why the professor is strict about this: when the external examiner asks you to show your Lab 0 work, "it's somewhere on the Desktop" is not an answer. One course folder, one lab subfolder, filenames exactly as printed on the next table — that habit is worth more marks across the semester than any single program.

THE COMPLETE FILE PLAN · 7 PROGRAMS

Four rehearsals at home, three performances in the lab.

Each prelab program mirrors one lab exercise on purpose — same shape, smaller stakes. Do the prelab honestly and lab day is déjà vu, not panic.

#	FILE (EXACT NAME)	WHEN	MECHANICS	REHEARSES FOR
1	`PrintName.java`	PRELAB · HOME	Scanner + println	Exercise 1
2	`SquareScanner.java`	PRELAB · HOME	Scanner + arithmetic	Exercise 2
3	`EvenOrOdd.java`	PRELAB · HOME	Scanner + if/else	Exercise 3
4	`CountEvens.java`	PRELAB · HOME	for + if + `count++`	Exercise 3's counters
5	`HelloStudent.java`	LAB DAY · EX 1	Scanner + println banner	—
6	`SimpleCalculator.java`	LAB DAY · EX 2	Scanner + all five arithmetic ops	—
7	`PassFailChecker.java`	LAB DAY · EX 3	array + for + if/else + `passCount++`/`failCount++`	—

The code on these lab pages cannot be selected or copied — by design. (This note appears once, here.)

Every solution sheet in every lab renders as non-copyable text. That is not meanness: the entire point of a warm-up lab is the path from your eyes through your fingers to the keyboard. Type every character, including the ones you think you'd never mistype. Muscle memory is the deliverable.

PRELAB THEORY · AT HOME · RULED NOTEBOOK OUT

Five questions before you touch the keyboard.

Pen first, always. The first three are guided — each carries a hint pointing back at the exact class that taught it. The last two are independent — no hint, because the exam won't bring one either. Model answers are on a later page, locked; earn them.

1TWO COMMANDSGUIDED

You have just saved PrintName.java in your lab-00 folder. Write the two commands, in order, that turn that file into output on the screen — and say in one phrase what each command does.

HINTClass 1's very first terminal: one command makes a new file, the other runs it. Which produces the .class?

YOUR RULED NOTEBOOK — WRITE BOTH COMMANDS + ONE PHRASE EACH

2NAME THE PARTSGUIDED

In the line int marks = kb.nextInt(); — name what each of the three pieces does: int marks, kb, and nextInt().

HINTClass 3's box-and-tag picture: one piece makes the box, one piece is the reader standing at the keyboard, one piece asks the reader for a specific shape of value.

YOUR RULED NOTEBOOK — THREE PIECES, ONE LINE EACH

3PREDICT THE OUTPUTGUIDED

What exactly does System.out.println(7 / 2); print — and why is the answer not 3.5?

HINTClass 4, Sheet 1, the hostel-mess division: what does int ÷ int do to the part after the decimal point — round it, or throw it away?

YOUR RULED NOTEBOOK — THE PRINTED VALUE + ONE-SENTENCE WHY

4WRITE THE CONDITIONINDEPENDENT

A number is stored in an int box called n. Write the exact condition — the part inside if (…) — that is true when n is even. No hint on this one.

YOUR RULED NOTEBOOK — THE CONDITION, CHARACTER BY CHARACTER

5COUNT THE RUNSINDEPENDENT

How many times does for (int i = 1; i <= 5; i++) run its body — and list every value i takes inside that body. No hint on this one either.

YOUR RULED NOTEBOOK — THE COUNT + EVERY VALUE OF i

Done all five in pen? Good. Don't peek ahead for answers — there are five more questions first, on the next page, and they're the ones lab day silently depends on.

PRELAB THEORY · FIVE MORE · THE ONES LAB DAY SILENTLY DEPENDS ON

Five more — one for each way lab day can bite.

How to use this page: same contract as before — pen answers in your ruled notebook, hints only on the guided three, nothing unlocked until you've committed ink. Each of these five rehearses a fluency the three lab exercises assume without saying so: the compile artefact, switch fall-through, off-by-one bounds, hand-tracing a counter, and what System.in actually is.

1CONCEPT RECALLGUIDED

In one sentence: what does javac produce, and where does that new file appear?

HINTAfter Class 1's first compile, you ran dir and saw one more file than you had typed. What was its extension, and which folder was it sitting in?

YOUR RULED NOTEBOOK — ONE SENTENCE, BOTH HALVES

2PREDICT THE OUTPUTGUIDED

Only case 3 has a break. day is 2. Write every line this prints, in order:

int day = 2;switch (day){ case 1: System.out.println("Mon"); case 2: System.out.println("Tue"); case 3: System.out.println("Wed"); break; case 4: System.out.println("Thu");}

HINTClass 4's mess-menu board: without break, execution falls through the floor of its case into the next one — where does the falling stop here?

YOUR RULED NOTEBOOK — EVERY PRINTED LINE, IN ORDER

3FIND THE BUGGUIDED

This loop was meant to print 1 to 10. It prints 1 to 11. Circle the exact characters at fault and write the fix:

for (int i = 1; i <= 11; i++){ System.out.println(i);}

HINTRead the middle slot of the for header out loud: "keep going while i is less than or equal to…" — to what?

YOUR RULED NOTEBOOK — THE FAULTY CHARACTERS + THE FIXED HEADER

4TRACE VARIABLESINDEPENDENT

Fill a pass-by-pass table for i and sum — one row per loop pass, then a final row for the printed value. No hint.

int i = 1, sum = 0;while (i <= 4){ sum = sum + i; i++;}System.out.println(sum);

YOUR RULED NOTEBOOK — TABLE: PASS · i · sum, THEN THE PRINT

5SHORT ANSWERINDEPENDENT

Why does Scanner need System.in as its argument — and not just in? Two sentences, your own words. No hint.

YOUR RULED NOTEBOOK — TWO SENTENCES

ITEM MIX · 1 × CONCEPT RECALL1 × PREDICT-OUTPUT1 × FIND-THE-BUG1 × TRACE1 × SHORT ANSWER

Bring this page to lab. Your tutor will spot-check two of these five at the door — in your handwriting, not on your screen. The model answers come next, locked; open them only after all ten questions carry ink.

SOLUTION SHEET · EXTRA FIVE · ANSWER + REASONING + THE COMMON SLIP

Model answers — extra five.

Per the solution-sheet contract, this page is separate from the questions on purpose — you cannot glance sideways at an answer. Each card gives the correct answer, the reasoning, the common slip with the real message your machine shows, and one sentence to keep.

All five answered in pen? Then compare — differences are findings, not failures.

MODEL ANSWER · Q1

1CONCEPT RECALL

Answer: javac produces a .class file of bytecode — for PrintName.java it creates PrintName.class — in the same folder you compiled from, your lab-00 working directory.
Reasoning: the compiler doesn't run anything; it translates your source into the JVM's language and writes that translation next to the source.
Common slip: saying "javac runs the program". Type javac PrintName.class and the real console answers error: file does not contain class PrintName.class — javac only eats .java.
Keep this: javac makes the .class; java runs it — two verbs, two commands.

MODEL ANSWER · Q2

2PREDICT THE OUTPUT

Answer: two lines — Tue then Wed — and nothing else.
Reasoning: day == 2 enters at case 2, prints Tue, finds no break, falls through into case 3, prints Wed, hits break, leaves. case 1 never entered; case 4 never reached.
Common slip: answering only Tue — treating every case as if it auto-stops. Java's switch keeps flowing until a break, the exact behaviour Class 4's MessMenu used on purpose.
Keep this: a case without break is a room without a floor.

MODEL ANSWER · Q3

3FIND THE BUG

Answer: the fault is the two characters 11 in the middle slot. Fix: for (int i = 1; i <= 10; i++) — or equivalently i < 11.
Reasoning: i <= 11 keeps the body alive when i is 11, so 11 prints. The loop's condition, not its intention, decides the last pass.
Common slip: "fixing" the wrong slot — changing i = 1 to i = 0, which prints 0…11: twelve lines, two of them wrong.
Keep this: off-by-one bugs live in the condition — read it aloud before you run.

MODEL ANSWER · Q4

4TRACE VARIABLES

Answer: Pass 1: i=1, sum=1 · Pass 2: i=2, sum=3 · Pass 3: i=3, sum=6 · Pass 4: i=4, sum=10 · then i becomes 5, 5 <= 4 is false, and it prints 10.
Reasoning: each pass adds the current i to sum before i++ steps it. One row per pass — exactly how you'll debug PassFailChecker if its counters drift.
Common slip: writing sum=1,2,3,4 — adding 1 each pass instead of adding i. If your last row says sum=4, you traced the ++ and not the +.
Keep this: trace what the line says, not what you'd have written.

MODEL ANSWER · Q5

5SHORT ANSWER

Answer: Scanner is a general reader — file, string or keyboard — so it must be told which source to read. System.in is the ready-made object representing the keyboard's input stream; a bare in is just an undeclared name.
Reasoning: in only means something as a field of the System class — the dot is the address.
Common slip: typing new Scanner(in). The real compiler says error: cannot find symbol — symbol: variable in. Java never guesses which in you meant.
Keep this: System.in is the keyboard, spelled with its full address.

SOLUTION SHEET · FIRST FIVE · ONE REVEAL PER QUESTION

Model answers — the first five, one at a time.

Same lock, same rule: ink first. Each question has its own reveal — open one only after that attempt exists in your notebook. Below the five, three slips that show up in every batch's Lab 0 — read them during the prelab so on lab day they're someone else's.

Your Q1 in pen first — then open this one, and only this one.

MODEL ANSWER · Q1 · TWO COMMANDS

1MODEL ANSWER

Answer: first javac PrintName.java, then java PrintName.
Reasoning: javac compiles your source into PrintName.class bytecode; java starts the JVM and runs that bytecode.
Common slip: java PrintName.java — the run command takes the class name with no extension in this workflow.
Keep this: javac eats a file, java eats a class.

MODEL ANSWER · Q2 · NAME THE PARTS

2MODEL ANSWER

int marks: makes an int-shaped box named marks.
kb: your Scanner object — the reader standing at the keyboard.
nextInt(): asks that reader to fetch the next whole number the user types and hand it over for storage in the box.
Keep this: box · reader · fetch — three parts, three jobs.

MODEL ANSWER · Q3 · PREDICT THE OUTPUT

3MODEL ANSWER

Answer: it prints 3.
Reasoning: both 7 and 2 are ints, so Java performs integer division and truncates the .5 — throws it away, no rounding — before println ever sees the value.
To get 3.5: put a double in the mix — 7 / 2.0.
Keep this: int ÷ int stays int; the decimal never existed.

MODEL ANSWER · Q4 · WRITE THE CONDITION

4MODEL ANSWER

Answer: if (n % 2 == 0)
Reasoning: the remainder after dividing by 2 is zero exactly when n is even.
Common slip: a single = — that's assignment, and the compiler rejects it here with error: incompatible types: int cannot be converted to boolean.
Keep this: both characters of == matter — one asks, one overwrites.

MODEL ANSWER · Q5 · COUNT THE RUNS

5MODEL ANSWER

Answer: the body runs 5 times, with i = 1, 2, 3, 4, 5.
Reasoning: when i++ makes i equal 6, the check 6 <= 5 fails and the loop ends.
The subtlety: i touches 6, but the body never sees it — the condition is checked before every pass.
Keep this: count the passes the condition lets through, not the values i visits.

AND THE 3 SLIPS EVERY BATCH MAKES — READ THESE NOW, NO LOCK

ASLIP 1 · THE FILENAME MISMATCH

The slip: saving printname.java for a class named PrintName.
Real message: error: class PrintName is public, should be declared in a file named PrintName.java
The rule: file name = class name, capital for capital — Windows forgives case, Java does not.

BSLIP 2 · COMPILING FROM THE WRONG FOLDER

The slip: your file is in lab-00 but your prompt says C:\Users\diya>.
Real message: error: file not found: PrintName.java
The rule: the terminal only sees the folder it is standing in — check the prompt before blaming the code.

CSLIP 3 · FORGETTING TO RECOMPILE

The slip: you edit the .java, run java PrintName again, and "nothing changed".
Why: nothing did — you re-ran the old .class. Every edit needs its javac before its java.
Rhythm to keep: edit, save, javac, java — in that order, every time.

PRELAB CODING · AT HOME · 20–25 MINUTES · NO CODE GIVEN — THAT'S THE POINT

Four small programs, each a rehearsal for one exercise.

Every task below is a mini problem statement: problem, requirements, a sample run to match, and a plan line for your notebook. No code on this page — you write it. The tutor solves all four live at the start of lab (next page), so arrive with attempts, not excuses.

ALL FOUR FILES GO HERE — EXACT NAMES FROM THE FILE PLAN C:\Users\<you>\Desktop\java-practice\lab-00\ holds: PrintName.java · SquareScanner.java · EvenOrOdd.java · CountEvens.java

TASK 1 · PRELABPrintName.javaRehearses Exercise 1 — the banner greeting

PROBLEM

Greet one student by name, the way Exercise 1 will greet them with a banner.

REQUIREMENTS

Class named exactly PrintName, saved as PrintName.java in lab-00.
Print the prompt Enter your name:
Read one word with Scanner's next().
Print exactly one line: Hello, followed by the name and !

SAMPLE RUN

user types Diya program prints Hello, Diya! — match it character for character, comma and space included.

PLAN

import class main Scanner prompt read println. Seven moves you've made since Class 3.

TASK 2 · PRELABSquareScanner.javaRehearses Exercise 2 — read, compute, print

PROBLEM

Read a number, do arithmetic on it, print the result. Exercise 2 does this five times over; you do it once in the prelab.

REQUIREMENTS

Class SquareScanner, saved as SquareScanner.java.
Prompt Enter a number:
Read one int with nextInt().
Print Square = followed by n × n.

SAMPLE RUN

user types 12 Square = 144.

PLAN

Identical skeleton to Task 1 — only the middle line changes: nextInt() instead of next(), and n*n in the println. Notice the reuse; that's the rehearsal working.

TASK 3 · PRELABEvenOrOdd.javaRehearses Exercise 3 — one decision, two roads

PROBLEM

One decision, two roads. Exercise 3's pass/fail check is this exact shape with different numbers.

REQUIREMENTS

Class EvenOrOdd, saved as EvenOrOdd.java.
Prompt Enter a number:
Read one int.
If it's even print EVEN, otherwise print ODD — using the very condition you wrote for theory Q4.

SAMPLE RUN

7 ODD · run it twice more with 0 and 44 — 0 must say EVEN.

PLAN

Skeleton read if (n % 2 == 0) two printlns in two branches. Test the boundary (0) — lab day will.

TASK 4 · PRELABCountEvens.javaRehearses Exercise 3 — the counting muscle, one day early

PROBLEM

Count how many of the numbers 1…20 are even. This is Exercise 3's passCount++ muscle, one day early.

REQUIREMENTS

Class CountEvens, saved as CountEvens.java.
No Scanner this time — a for loop from 1 to 20.
Inside it, an if with your even condition and count++ when it's true.
After the loop, print Evens found: and the count.

SAMPLE RUN

exactly one line: Evens found: 10 — if you see 11, revisit theory Q3; your bounds slipped.

PLAN

declare int count = 0 BEFORE the loop (Class 4's Act 5 taught you why — scope ends at the brace) loop if count++ println after.

Stuck for more than 15 minutes on one task?

Stop, write in your notebook which line refused to work and what the console said, and move to the next task. A precise description of where you got stuck earns walkthrough attention on lab day; a blank folder earns nothing.

LAB DAY · FIRST 25 MINUTES · TUTOR AT THE FRONT MACHINE

The walkthrough — your four rehearsals, solved live.

Lab day opens with your tutor building all four prelab programs on the projector, one line per press. Compare each against your homework version as it grows — differences in variable names are taste; differences in structure are your revision list.

WALKTHROUGH 1 OF 4 · Scanner + println

MINI PROBLEM · PRINTNAME.JAVA · YOUR TASK 1, SOLVED LIVE

PROBLEM

Greet one student by name — the Task 1 rehearsal you built at home, now on the projector.

REQUIREMENTS

Class PrintName; prompt Enter your name: with print (cursor waits on the same line).
Read one word with next(); print Hello, + name + !

EXPECTED OUTPUT

user types Diya — program answers Hello, Diya! — comma and space exactly.

SAVE AS · EXACT NAME, EXACT FOLDER C:\Users\<you>\Desktop\java-practice\lab-00\PrintName.java

 PrintName.java — Notepad++
1import java.util.Scanner;
2public class PrintName
3{
4    public static void main(String[] args)
5    {
6        Scanner kb = new Scanner(System.in);
7        System.out.print("Enter your name: ");
8        String name = kb.next();
9        System.out.println("Hello, " + name + "!");
10    }
11}

COMMAND PROMPT — RUN FROM THE LAB-00 FOLDER

C:\Users\diya\Desktop\java-practice\lab-00> javac PrintName.java

C:\Users\diya\Desktop\java-practice\lab-00> java PrintName

Enter your name: Diya

Hello, Diya!

Line 7 used print, not println — so the cursor waits on the same line as the prompt. Small detail, professional feel. ✦

WALKTHROUGH 2 OF 4 · Scanner + arithmetic

MINI PROBLEM · SQUARESCANNER.JAVA · YOUR TASK 2, SOLVED LIVE

PROBLEM

Read a number, compute its square, print it — the read-compute-print rhythm Exercise 2 repeats five times.

REQUIREMENTS

Class SquareScanner; prompt Enter a number: ; read one int with nextInt().
Print Square = followed by n × n.

EXPECTED OUTPUT

user types 12 — program answers Square = 144.

SAVE AS · EXACT NAME, EXACT FOLDER C:\Users\<you>\Desktop\java-practice\lab-00\SquareScanner.java

 SquareScanner.java — Notepad++
1import java.util.Scanner;
2public class SquareScanner
3{
4    public static void main(String[] args)
5    {
6        Scanner kb = new Scanner(System.in);
7        System.out.print("Enter a number: ");
8        int n = kb.nextInt();
9        System.out.println("Square = " + n * n);
10    }
11}

COMMAND PROMPT — SAME FOLDER, SAME RHYTHM

C:\Users\diya\Desktop\java-practice\lab-00> javac SquareScanner.java

C:\Users\diya\Desktop\java-practice\lab-00> java SquareScanner

Enter a number: 12

Square = 144

Why 144 and not "Square = 12*12"? Because * binds tighter than + — multiplication first, then the string glue. Class 4's ladder, already earning rent. ✦

WALKTHROUGH 3 OF 4 · Scanner + if/else

MINI PROBLEM · EVENORODD.JAVA · YOUR TASK 3, SOLVED LIVE

PROBLEM

One decision, two roads — Exercise 3's pass/fail check wearing smaller numbers.

REQUIREMENTS

Class EvenOrOdd; prompt Enter a number: ; read one int.
if (n % 2 == 0) print EVEN, otherwise print ODD.

EXPECTED OUTPUT

two runs: 7 gives ODD · 0 gives EVEN (the boundary must behave).

SAVE AS · EXACT NAME, EXACT FOLDER C:\Users\<you>\Desktop\java-practice\lab-00\EvenOrOdd.java

 EvenOrOdd.java — Notepad++
1import java.util.Scanner;
2public class EvenOrOdd
3{
  public static void main(String[] args)
  {
      Scanner kb = new Scanner(System.in);
      System.out.print("Enter a number: ");
      int n = kb.nextInt();
      if (n % 2 == 0)
      {
          System.out.println("EVEN");
      }
      else
      {
          System.out.println("ODD");
      }
  }
18}

COMMAND PROMPT — THREE RUNS, ONE BOUNDARY

C:\Users\diya\Desktop\java-practice\lab-00> javac EvenOrOdd.java

C:\Users\diya\Desktop\java-practice\lab-00> java EvenOrOdd

Enter a number: 7

ODD

C:\Users\diya\Desktop\java-practice\lab-00> java EvenOrOdd

Enter a number: 0

EVEN

Ran twice — no recompile between runs, because the code didn't change. And 0 says EVEN: 0 % 2 is 0. The boundary behaves. ✦

WALKTHROUGH 4 OF 4 · for + if + count++ (EXERCISE 3'S MUSCLE)

MINI PROBLEM · COUNTEVENS.JAVA · YOUR TASK 4, SOLVED LIVE

PROBLEM

Count how many of the numbers 1…20 are even — the exact passCount++ counting muscle Exercise 3 needs.

REQUIREMENTS

Class CountEvens; no Scanner — a for loop from 1 to 20.
Declare int count = 0; BEFORE the loop; count++ inside an if with the even condition.
After the loop, print Evens found: and the count.

EXPECTED OUTPUT

exactly one line: Evens found: 10 — 11 means your bounds slipped.

SAVE AS · EXACT NAME, EXACT FOLDER C:\Users\<you>\Desktop\java-practice\lab-00\CountEvens.java

 CountEvens.java — Notepad++
1public class CountEvens
2{
  public static void main(String[] args)
  {
      int count = 0;                // BEFORE the loop — scope lives past the brace
      for (int i = 1; i <= 20; i++)
      {
          if (i % 2 == 0)
          {
              count++;             // the exact passCount++ muscle for Ex 3
          }
      }
      System.out.println("Evens found: " + count);
  }
15}

COMMAND PROMPT — ONE LINE OUT, EXACTLY

C:\Users\diya\Desktop\java-practice\lab-00> javac CountEvens.java

C:\Users\diya\Desktop\java-practice\lab-00> java CountEvens

Evens found: 10

If your homework printed 11, your loop header said <= 21 or started at 0 — the theory-Q3 bug wearing a different shirt. Fix it now, before Exercise 3 inherits it. ✦

Walkthrough over — screens down. From here the projector goes dark and the next three briefs are yours alone. Everything you're about to type, you have now seen twice: once in class, once on this wall.

EXERCISE 1 OF 3 · 15 MINUTES · 20 MARKS · YOU ALONE

Exercise 1 — HelloStudent.java

No code on this screen — that's deliberate. You built PrintName.java at home and watched it again twenty minutes ago. Same shape, one extra read, one banner.

SAVE AS · EXACT NAME, EXACT FOLDER — BEFORE YOU TYPE A LINE C:\Users\<you>\Desktop\java-practice\lab-00\HelloStudent.java

PROBLEM The lab's attendance system greets each student with a three-line banner built from their own details.

REQUIREMENTS ① Class named exactly HelloStudent. ② Prompt Enter your name: and read one word. ③ Prompt Enter your roll number: and read one int. ④ Print exactly three lines: a row of ten = signs · Welcome, name (Roll roll) · the same = row again.

SAMPLE RUN inputs Diya and 41 must produce:

TARGET OUTPUT — MATCH CHARACTER FOR CHARACTER

Enter your name: Diya
Enter your roll number: 41
==========
Welcome, Diya (Roll 41)
==========

PLAN FIRST — LIST YOUR main() LINES IN ORDER, IN PEN, BEFORE NOTEPAD++

Reminder: name + int reads in this order behave — the reverse can bite.

You read the name with next() first, then the roll with nextInt(). Keep that order. (The full story of nextLine() after nextInt() is a Class 27 topic — today, just follow the brief.)

SOLUTION SHEET · EXERCISE 1 · AFTER YOUR ATTEMPT COMPILES — OR 15 MINUTES, WHICHEVER FIRST

HelloStudent, line by line.

Locked until you've fought for it. Open, then compare structure: your line order can differ; your output cannot.

Attempted honestly? Compiler consulted at least once? Then open.

SOLUTION · HelloStudent.java · SAVED IN C:\Users\diya\Desktop\java-practice\lab-00\

 HelloStudent.java — Notepad++
1import java.util.Scanner;
2public class HelloStudent
3{
4    public static void main(String[] args)
5    {
6        Scanner kb = new Scanner(System.in);
7        System.out.print("Enter your name: ");
8        String name = kb.next();
9        System.out.print("Enter your roll number: ");
10        int roll = kb.nextInt();
11        System.out.println("==========");
12        System.out.println("Welcome, " + name + " (Roll " + roll + ")");
13        System.out.println("==========");
14    }
15}

COMMAND PROMPT — THE PROOF

C:\Users\diya\Desktop\java-practice\lab-00> javac HelloStudent.java

C:\Users\diya\Desktop\java-practice\lab-00> java HelloStudent

Enter your name: Diya

Enter your roll number: 41

==========

Welcome, Diya (Roll 41)

==========

Line 12 glues four pieces with +. Java turns roll's int into text the moment a String joins the chain — Class 3's + rule doing exercise-1 work. ✦

EXERCISE 2 OF 3 · 20 MINUTES · 30 MARKS · YOU ALONE

Exercise 2 — SimpleCalculator.java

SquareScanner read one number and did one operation. This reads two numbers and reports five operations — including the two whose int behaviour Class 4 made you trace in ink.

SAVE AS · EXACT NAME, EXACT FOLDER — BEFORE YOU TYPE A LINE C:\Users\<you>\Desktop\java-practice\lab-00\SimpleCalculator.java

PROBLEM A two-number calculator for the lab bench: read a and b, print the five arithmetic results, clearly labelled.

REQUIREMENTS ① Class named exactly SimpleCalculator. ② Prompts Enter a: and Enter b:, both read as ints. ③ Five labelled output lines: Sum, Difference, Product, Quotient, Remainder — in that order, format Label = value. ④ Use a = 17, b = 5 for your first test and check the last two lines against your Class 4 knowledge before running.

SAMPLE RUN inputs 17 and 5 must produce:

TARGET OUTPUT — PREDICT THE LAST TWO LINES IN PEN FIRST

Enter a: 17
Enter b: 5
Sum = 22
Difference = 12
Product = 85
Quotient = 3
Remainder = 2

BEFORE YOU RUN — WHY IS THE QUOTIENT 3 AND NOT 3.4? ONE SENTENCE, PEN.

SOLUTION SHEET · EXERCISE 2

SimpleCalculator, line by line.

Five printlns, one pattern — and the two "dangerous" lines are only dangerous if you expected decimals from int boxes.

Your five lines printed something? Compare now — especially the last two.

SOLUTION · SimpleCalculator.java · SAVED IN C:\Users\diya\Desktop\java-practice\lab-00\

 SimpleCalculator.java — Notepad++
1import java.util.Scanner;
2public class SimpleCalculator
3{
  public static void main(String[] args)
  {
      Scanner kb = new Scanner(System.in);
      System.out.print("Enter a: ");
      int a = kb.nextInt();
      System.out.print("Enter b: ");
      int b = kb.nextInt();
      System.out.println("Sum = " + (a + b));
      System.out.println("Difference = " + (a - b));
      System.out.println("Product = " + a * b);
      System.out.println("Quotient = " + a / b);      // int ÷ int — truncates
      System.out.println("Remainder = " + a % b);     // the leftover
  }
17}

COMMAND PROMPT — THE PROOF

C:\Users\diya\Desktop\java-practice\lab-00> javac SimpleCalculator.java

C:\Users\diya\Desktop\java-practice\lab-00> java SimpleCalculator

Enter a: 17

Enter b: 5

Sum = 22

Difference = 12

Product = 85

Quotient = 3

Remainder = 2

Why brackets on lines 11–12 but not 13–15? Without them, + would glue "Sum = " to a first, then to b — printing 175. Only + is ambiguous like this; * / % bind tighter than the string +. ✦

If your Sum line printed Sum = 175 — that's the finding of the day.

"Sum = " + a + b runs left to right: string + 17 makes "Sum = 17", then + 5 glues "5". The brackets in ("Sum = " + (a + b)) force the arithmetic first. Write this one in your notebook; it returns in the exam.

EXERCISE 3 OF 3 · 25 MINUTES · 30 MARKS · THE ONE THAT USES EVERYTHING

Exercise 3 — PassFailChecker.java

Array + for + if/else + two counters. Every piece rehearsed: the array from Class 3, the loop-and-if from CountEvens, the two-road decision from EvenOrOdd. Now they work one shift together.

SAVE AS · EXACT NAME, EXACT FOLDER — BEFORE YOU TYPE A LINE C:\Users\<you>\Desktop\java-practice\lab-00\PassFailChecker.java

PROBLEM Six students' marks are already known. The class teacher wants each verdict printed, then a two-line summary of how many passed and failed.

REQUIREMENTS ① Class named exactly PassFailChecker. ② Start from this array — type it exactly: int[] marks = { 62, 34, 78, 40, 91, 25 }; ③ Pass mark is 40 or above. ④ For each student print Student 1: 62 - PASS style lines (numbering from 1, not 0). ⑤ Declare passCount and failCount before the loop; step the right one in each branch. ⑥ After the loop, print Passed: and Failed: lines.

SAMPLE RUN with the given array, exactly this:

TARGET OUTPUT — COUNT THE PASSES IN PEN BEFORE CODING: IS 40 A PASS?

Student 1: 62 - PASS
Student 2: 34 - FAIL
Student 3: 78 - PASS
Student 4: 40 - PASS
Student 5: 91 - PASS
Student 6: 25 - FAIL
Passed: 4
Failed: 2

PLAN FIRST — WHICH CONDITION MAKES 40 A PASS: > 40 OR >= 40? AND WHY DOES Student 1 PRINT marks[0]?

SOLUTION SHEET · EXERCISE 3

PassFailChecker, line by line.

Watch the two counters and the i + 1 label — the two places this exercise decides your marks.

Eight lines of output matching the target? Then this is just a victory lap.

SOLUTION · PassFailChecker.java · SAVED IN C:\Users\diya\Desktop\java-practice\lab-00\

 PassFailChecker.java — Notepad++
1public class PassFailChecker
2{
  public static void main(String[] args)
  {
      int[] marks = { 62, 34, 78, 40, 91, 25 };
      int passCount = 0, failCount = 0;   // BEFORE the loop — CountEvens taught you why
      for (int i = 0; i < marks.length; i++)
      {
          if (marks[i] >= 40)
          {
              System.out.println("Student " + (i + 1) + ": " + marks[i] + " - PASS");
              passCount++;
          }
          else
          {
              System.out.println("Student " + (i + 1) + ": " + marks[i] + " - FAIL");
              failCount++;
          }
      }
      System.out.println("Passed: " + passCount);
      System.out.println("Failed: " + failCount);
  }
23}

COMMAND PROMPT — THE PROOF

C:\Users\diya\Desktop\java-practice\lab-00> javac PassFailChecker.java

C:\Users\diya\Desktop\java-practice\lab-00> java PassFailChecker

Student 1: 62 - PASS

Student 2: 34 - FAIL

Student 3: 78 - PASS

Student 4: 40 - PASS

Student 5: 91 - PASS

Student 6: 25 - FAIL

Passed: 4

Failed: 2

Student 4 with exactly 40 passes — because line 9 says >=, not >. One character, one student's semester. Boundaries are where marks live. ✦

LAST 10 MINUTES · DEBRIEF, MARKS & WHAT LEAVES THE ROOM WITH YOU

Six mistakes, one rubric, one folder to show.

Before you log off: the six mistakes this lab sees every single year — check yourself against each — then how the 100 marks split, and exactly what to submit.

#	THE MISTAKE	WHAT THE MACHINE SAYS / SHOWS	THE FIX
1	File name ≠ class name (`hellostudent.java`)	`class HelloStudent is public, should be declared in a file named HelloStudent.java`	Match capital for capital, always
2	Compiling from the wrong folder	`error: file not found`	Read your prompt — it must end in `lab-00>`
3	`java HelloStudent.java` after javac	`error: could not find or load main class HelloStudent.java`	`java HelloStudent` — class name, no extension
4	`=` instead of `==` in the pass check	`incompatible types: int cannot be converted to boolean`	Comparison is always two characters
5	Counters declared inside the loop	Compiles… then `Passed: 0` or `cannot find symbol` at the println	Declare before the loop — scope dies at `}`
6	`"Sum = " + a + b` without brackets	Prints `Sum = 175` — no error at all, just wrong	Bracket the arithmetic: `(a + b)`

Notice something about those six? Only one of them is about "not knowing Java". The other five are discipline: naming, folders, commands, scope, brackets. That is why the prelab exists — and why next lab assumes all six are behind you.

THE 100 MARKS · KNOW WHERE THEY LIVE BEFORE THE EXAMINER ASKS

COMPONENT	MARKS	WHAT EARNS FULL MARKS
Prelab · 10 theory Qs in ink	10	All ten attempted in your ruled notebook, before lab day — checked at the door
Prelab · 4 programs	10	Four .java files in your `lab-00` folder, each compiled at least once (the .class is the proof)
Exercise 1 · HelloStudent	20	Compiles · output matches the target exactly · file named right
Exercise 2 · SimpleCalculator	30	Compiles · all five lines labelled and correct · you can explain Quotient = 3 when asked
Exercise 3 · PassFailChecker	30	Compiles · all 8 lines match · counters declared before the loop · you can explain the `i + 1`

"You can explain" is in the rubric on purpose.

The examiner will point at one line of your own program and ask why. A working program you can't explain scores like a borrowed one — because it is one.

WHAT TO SUBMIT — YOUR FOLDER AT THE END OF THE SESSION

C:\Users\diya\Desktop\java-practice\lab-00\ — 14 FILES, EXACTLY

Desktop\java-practice\lab-00\

PrintName.java + .class <- prelab 1

SquareScanner.java + .class <- prelab 2

EvenOrOdd.java + .class <- prelab 3

CountEvens.java + .class <- prelab 4

HelloStudent.java + .class <- exercise 1 · 20 marks

SimpleCalculator.java + .class <- exercise 2 · 30 marks

PassFailChecker.java + .class <- exercise 3 · 30 marks

1 Submit: the lab-00 folder + your ruled notebook

Folder zipped or copied as your lab instructor directs; notebook open to the ten theory answers. Both leave the room checked today — nothing is "emailed later".

2 Debrief line, in pen, before you stand up

Complete this sentence in your notebook: "The mistake that cost me the most time today was ______, and next lab I will ______." One honest line — it's the cheapest marks-insurance you'll ever write.

MY LAB 0 FOLDER · YOUR PROGRAMS, READY TO SUBMIT AS ONE PDF

Write each program in its own box on this page and press Compile & Run until it works. When it compiles and runs, it saves itself here with a green tick — a later working run replaces the saved copy. At the end, type your name and roll number below and press Download all programs (PDF). That PDF is what you submit.

NEXT · CLASS 5 · PART C BEGINS · JAVA THE LANGUAGE

You've typed Java. Now meet Java.

Part C opens the story: James Gosling, the twelve buzzwords, and why this language you've now sweated in looks the way it does — Java against C++, Python and C#, argued properly.

Class 4 · Operators & control flow Unit 1 overview

Everything is taught.Now you type.

Four rehearsals at home, three performances in the lab.

Five questions before you touch the keyboard.

Five more — one for each way lab day can bite.

Model answers — extra five.

Model answers — the first five, one at a time.

Four small programs, each a rehearsal for one exercise.

The walkthrough — your four rehearsals, solved live.

Exercise 1 — HelloStudent.java

HelloStudent, line by line.

Exercise 2 — SimpleCalculator.java

SimpleCalculator, line by line.

Exercise 3 — PassFailChecker.java

PassFailChecker, line by line.

Six mistakes, one rubric, one folder to show.

You've typed Java. Now meet Java.

Everything is taught.
Now you type.