Operators in Java ICSE Class 9: Types, Precedence, Increment and Decrement

What Operators in Java is about

Weightage: CISCE publishes no chapter weightage and no question-paper layout for ICSE Class 9 Computer Applications. Class IX is examined by your school: one 100-mark theory paper of 2 hours, plus 100 marks of internal assessment (at least 15 programming assignments and a written project on ethical computing). This is topic 4 of the 2028 syllabus.Source: CISCE ICSE 2028 Computer Applications syllabus, Class IX

Key concepts

Forms of operators: unary, binary, ternary

An operand is a value or variable on which an operator acts. Operators are classified by the number of operands:

• Unary operators act on one operand: unary minus (−a), unary plus (+a), increment (++), decrement (--), logical NOT (!).
• Binary operators act on two operands: + − * / % (arithmetic), < > <= >= == != (relational), && || (logical), = and += etc. (assignment).
• Ternary operator acts on three operands: the conditional operator ?:

The conditional (ternary) operator:
condition ? value-if-true : value-if-false
int big = (m > n) ? m : n; // with m = 8, n = 12, big = 12
String res = marks >= 40 ? "Pass" : "Fail"; // with marks = 72: Pass
It is a compact replacement for a simple if-else that chooses a value.

Worked example

(2 marks) Rewrite using the ternary operator: if (a > b) max = a; else max = b;

Try it first, then show the solutionSolution

1. Condition a > b; true value a; false value b - 1 mark.
2. max = (a > b) ? a : b; - 1 mark.

Answer: max = (a > b) ? a : b;

Arithmetic, relational and logical operators

Arithmetic: + (add), − (subtract), * (multiply), / (divide), % (modulus: remainder).

• Integer division drops the fraction: 7 / 2 = 3; −7 / 2 = −3.
• % gives the remainder and takes the sign of the left operand: 17 % 5 = 2; −17 % 5 = −2; 17 % −5 = 2. It also works on decimals: 5.5 % 2 = 1.5.
• Uses of %: test even/odd (n % 2 == 0), extract the last digit (n % 10), test divisibility.

Relational (comparison): < > <= >= == != . They compare two values and give a boolean (true or false): 5 > 3 is true. Note == compares; = assigns.

Logical: combine or reverse boolean conditions.

• && (AND): true only if both are true.
• || (OR): true if at least one is true.
• ! (NOT): reverses the value.

Short-circuit evaluation: in A && B, if A is false, B is not evaluated; in A || B, if A is true, B is not evaluated. As run in this study guide:
int p = 5; boolean r = (p > 10) && (++p > 5); gives r = false, p = 5 (++p never ran).
int q = 5; boolean s = (q > 1) || (++q > 5); gives s = true, q = 5.

Worked example

(2 marks) Give the output: System.out.println(17 % 5 + " " + (-17 % 5) + " " + (17 % -5) + " " + 5.5 % 2);

Try it first, then show the solutionSolution

1. 17 % 5 = 2; −17 % 5 = −2 (sign of the left operand) - 1 mark.
2. 17 % −5 = 2; 5.5 % 2 = 1.5 - 1 mark.

Answer: 2 -2 2 1.5

Assignment and shorthand operators; counters and accumulators

Assignment operator =: stores the value on the right in the variable on the left: x = 5;

Shorthand (compound assignment) operators combine an arithmetic operation with assignment: += −= *= /= %=
a += 3 means a = a + 3; i *= 2 + 3 means i = i * (2 + 3): the whole right side is worked out first. With i = 7, i *= 2 + 3 gives 35.
Shorthand operators include an automatic cast: char ch = 'a'; ch += 2; gives 'c' (whereas ch = ch + 2; does not compile).

Counter: a variable that counts how many times something happens; it starts at 0 and increases by 1 each time: count = count + 1; or count++;
Accumulator: a variable that collects a running total; it starts at 0 (or 1 for a product) and adds each new value: sum = sum + x; or sum += x;
As run in this study guide (three values 15, 25, 35):
count = count + 1; sum = sum + 15;
count++; sum += 25;
count++; sum += 35;
count = 3, sum = 75, average = (double) sum / count = 25.0
In later chapters counters and accumulators are used inside loops.

Worked example

(2 marks) Distinguish between a counter and an accumulator with an example of each.

Try it first, then show the solutionSolution

1. Counter: counts occurrences, increased by 1, e.g. count++ - 1 mark.
2. Accumulator: builds a running total, increased by a value, e.g. sum += marks - 1 mark.

Answer: A counter records how many times an event occurs and is increased by 1 each time (count++). An accumulator stores a running total and is increased by each new value (sum = sum + marks).

Increment and decrement: prefix and postfix

++ adds 1 and -- subtracts 1 from a variable. Each has two forms:

• Prefix (++a, --a): change first, then use. The new value is used in the expression.
• Postfix (a++, a--): use first, then change. The old value is used in the expression, and the variable is changed afterwards.

On its own as a statement (a++; or ++a;) both simply add 1.

Traces (as run in this study guide):
1. int a = 5; int b = a++ + ++a;
a++ gives 5 (a becomes 6); ++a makes a 7 and gives 7; b = 5 + 7 = 12; a = 7.
2. int k = 4; int y = k-- * 2 + --k;
k-- gives 4 (k becomes 3); 4 * 2 = 8; --k makes k 2 and gives 2; y = 10; k = 2.
3. int x = 10; x += x++ + --x;
The old x (10) is saved for the +=; x++ gives 10 (x becomes 11); --x gives 10; right side = 20; x = 10 + 20 = 30.
4. int z = 3; z = z++ + z++; gives 3 + 4 = 7.

Method: work strictly left to right, writing the value used and the new value of the variable at each step.

Worked example

(2 marks) Give the values of a and b: int a = 5; int b = a++ + ++a;

Try it first, then show the solutionSolution

1. a++ uses 5, then a = 6; ++a makes a = 7 and uses 7 - 1 mark.
2. b = 5 + 7 = 12; a = 7 - 1 mark.

Answer: a = 7, b = 12

Precedence and associativity

Precedence (hierarchy) decides which operator is applied first when an expression has several. Associativity decides the order when operators of the same precedence appear together.

Order used in ICSE (highest first):
1. ( ) brackets, . dot, postfix ++ --
2. Unary: prefix ++ --, unary + −, ! (right to left)
3. * / % (left to right)
4. + − (left to right)
5. < <= > >=
6. == !=
7. &&
8. ||
9. ?: (right to left)
10. = += −= *= /= %= (right to left)

Examples (as run in this study guide):

• 2 + 3 * 4 = 14 (multiplication first); (2 + 3) * 4 = 20.
• 10 − 4 − 3 = 3 (left to right: 6 − 3).
• 100 / 10 / 2 = 5 (left to right: 10 / 2).
• 8 / 3 * 3 + 8 % 3 = 2 * 3 + 2 = 8.
• 10 + 20 + "30" + 40 + 50 prints 30304050: 10 + 20 = 30 first, then everything after the String is joined as text.

Assignment is right to left: a = b = 5 sets b, then a.

Worked example

(2 marks) Evaluate: 8 / 3 * 3 + 8 % 3

Try it first, then show the solutionSolution

1. * / % have equal precedence, left to right: 8 / 3 = 2; 2 * 3 = 6; 8 % 3 = 2 - 1 mark.
2. Then + : 6 + 2 = 8 - 1 mark.

Answer: 8

new and dot operators; print() and println()

new operator: creates an object dynamically, that is, allocates memory for it while the program runs, and returns a reference to it.
Student s = new Student();
Scanner sc = new Scanner(System.in);

Dot (.) operator: accesses (invokes) the members of a class or object: s.name, s.show(), Math.sqrt(16), System.out.println().

Output statements:

• System.out.print(x): prints x and leaves the cursor on the same line.
• System.out.println(x): prints x and then moves the cursor to the next line. System.out.println(); alone prints a blank line.
• The + operator joins (concatenates) text with values: "Sum = " + s.

Program (as run in this study guide): splitting seconds with / and %.
class TimeSplit
{
public static void main(String args[])
{
int total = 7384;
int hours = total / 3600;
int rest = total % 3600;
int minutes = rest / 60;
int seconds = rest % 60;
System.out.println(total + " seconds = " + hours + " h " + minutes + " min " + seconds + " s");
}
}
Output: 7384 seconds = 2 h 3 min 4 s

Worked example

(2 marks) What is the role of the new operator in Student s = new Student(); and of the dot operator in s.show();?

Try it first, then show the solutionSolution

1. new allocates memory for a Student object at run time and returns its reference, stored in s - 1 mark.
2. The dot operator accesses the member method show() of the object s - 1 mark.

Answer: new creates a Student object in memory during execution and returns its reference, which is stored in s. In s.show(); the dot operator invokes the method show() belonging to the object s.

Operators in Java in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Arithmetic, Relational and Logical Operators with Short-Circuit Evaluation
• Increment, Decrement, Shorthand Operators, Precedence, new and Dot

Operators in Java: syntax and key facts

Forms

Unary (1 operand): ++ -- ! −; binary (2): + − * / % < == && =; ternary (3): ?:

condition ? a : b

Prefix vs postfix

++a: change then use; a++: use then change

Trace left to right.

Shorthand

a op= b means a = a op (b)

i *= 2 + 3 → i = i * 5.

Precedence (high to low)

1. 1.() . postfix
2. 2.unary ! ++ --
3. 3.* / %
4. 4.+ −
5. 5.< > <= >=
6. 6.== !=
7. 7.&&
8. 8.||
9. 9.?:
10. 10.= op=

Same level: left to right (except unary, ?:, assignment).

Integer rules

int / int = int (fraction dropped); a % b has the sign of a

7 / 2 = 3; −17 % 5 = −2.

How the school exam asks Operators in Java

The question patterns to expect, and the method that works for each.

Tricks to remember Operators in Java

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Pre = Prepare first

  Prefix: prepare (change) the value first, then use it; postfix: post (after) use, change.

  Use it when: Prefix vs postfix.

• BUMA RELAT

  Brackets, Unary, Multiplicative, Additive, RElational, Logical (&& before ||), Assignment Too.

  Use it when: Precedence order.

• Mod takes the left sign

  The sign of a % b follows a.

  Use it when: Negative modulus.

Operators in Java: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section B style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 7-mark question split into 3 + 2 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Operators in Java

The slips examiners see most often, and what to write instead.

• ✗Mistake: Using the new value in a postfix expression

  Prefix and postfix confused.

  Wrong working

  int a = 5; b = a++ * 2; gives b = 12

  Right working

  a++ uses 5 first: b = 10, then a = 6.

  ✓Do this: Postfix: use, then change.

  Usually costs: 1 to 2 marks.

• ✗Mistake: Ignoring integer division

  Expecting decimals from int operands.

  Wrong working

  7 / 2 = 3.5

  Right working

  7 / 2 = 3; 7 / 2.0 = 3.5

  ✓Do this: If both operands are int, the result is int.

  Usually costs: 1 mark.

• ✗Mistake: Evaluating string joins numerically throughout

  + has two meanings.

  Wrong working

  10 + 20 + "30" + 40 prints 100

  Right working

  Prints 303040: numbers add until a String appears, then everything joins.

  ✓Do this: Work left to right and switch to joining after the first String.

  Usually costs: 1 mark.

• ✗Mistake: Writing bitwise & or | for logical AND/OR

  Single symbols look similar.

  ✓Do this: Use && and || in conditions; bitwise operators are not in the syllabus.

  Usually costs: 1 mark.

Practice questions on Operators in Java

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   The value of 15 % 4 * 2 is:
   (a) 6
   (b) 1
   (c) 2
   (d) 7

   Hint

   Left to right.

   Answer

   (a) 6 (15 % 4 = 3; 3 * 2 = 6)

2. Q2 · 1 mark · MCQExam level

   Which operator has the highest precedence among these?
   (a) &&
   (b) +
   (c) !
   (d) ==

   Hint

   Unary.

   Answer

   (c) !

3. Q3 · 2 marks · Very short answerHarder exam level

   Give the output: int z = 3; z = z++ + z++; System.out.println(z);

   Hint

   3 then 4.

   Answer

   7 (first z++ uses 3, z becomes 4; second uses 4; 3 + 4 = 7 assigned to z).

4. Q4 · 2 marks · Very short answerHarder exam level

   Give the output: int q = 5; boolean s = (q > 1) || (++q > 5); System.out.println(s + " " + q);

   Hint

   OR stops at the first true.

   Answer

   true 5

5. Q5 · 2 marks · Very short answerHarder exam level

   Rewrite using shorthand operators: (i) a = a * 4; (ii) b = b % 10; (iii) c = c - (d + 2);

   Hint

   op=

   Answer

   (i) a *= 4; (ii) b %= 10; (iii) c -= d + 2;

6. Q6 · 2 marks · Short answerHOTS / competency

   Give the output: System.out.println(-7 / 2 + " " + 7 / 2 * 2.0);

   Hint

   Integer division first.

   Answer

   -3 6.0 (−7 / 2 = −3; 7 / 2 = 3, then 3 * 2.0 = 6.0)

7. Q7 · 2 marks · Very short answerExam level

   Distinguish between = and == with an example.

   Hint

   Assign vs compare.

   Answer

   = is the assignment operator that stores a value (x = 5;). == is a relational operator that compares two values and gives true or false (x == 5).

8. Q8 · 15 marks · Long answerHarder exam level

   Write a program to store a three-digit number 472 and print the sum of its digits using / and %.

   Hint

   n % 10 gives the last digit.

   Answer

   class DigitSum
   {
   public static void main(String args[])
   {
   int n = 472;
   int units = n % 10;
   int tens = (n / 10) % 10;
   int hundreds = n / 100;
   int sum = units + tens + hundreds;
   System.out.println("Digits: " + hundreds + ", " + tens + ", " + units);
   System.out.println("Sum of digits = " + sum);
   }
   }
   Output (as run):
   Digits: 4, 7, 2
   Sum of digits = 13

9. Q9 · 2 marks · Short answerHOTS / competency

   A student writes int avg = (m1 + m2 + m3) / 3; for marks 70, 75 and 81 and gets 75. The correct average is 75.33. Explain the error and correct it.

   Hint

   Integer division and type.

   Answer

   Both the sum (226) and 3 are int, so the division drops the fraction, and avg is int anyway. Correct: double avg = (m1 + m2 + m3) / 3.0; which gives 75.33...

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Result of 17 % 5?Show answer

   2

2. 2.Operator that creates an object?Show answer

   new

3. 3.a += b is short for?Show answer

   a = a + b

4. 4.Which is evaluated first: && or ||?Show answer

   &&

5. 5.Number of operands of ?:?Show answer

   Three.

6. 6.Difference between print() and println()?Show answer

   println() moves to a new line after printing; print() does not.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Unary (1), binary (2), ternary ?: (3 operands).
• ☐Arithmetic + − * / %; int / int drops the fraction; % takes the sign of the left operand.
• ☐Relational give boolean; logical && || ! with short-circuiting.
• ☐++a change then use; a++ use then change.
• ☐Precedence: () → unary → * / % → + − → relational → equality → && → || → ?: → assignment.
• ☐new creates objects; dot accesses members; print stays, println moves to a new line.

Operators in Java: frequently asked questions