Unary operators in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pre-increment and post-increment

What is the output of the following Java code?

Java

int x = 5;
System.out.println(x++);
System.out.println(++x);

A 5\n7

B 6\n7

C 5\n6

D 6\n6

💡 Hint

Remember that x++ returns the value before incrementing, while ++x increments first then returns.

The first print outputs 5 because x++ returns the current value then increments. After that, x becomes 6. The second print uses ++x, which increments x to 7 first, then prints 7.

❓ Predict Output

intermediate

Output of unary minus and plus operators

What is the output of this Java code snippet?

Java

int a = 10;
int b = -a;
int c = +b;
System.out.println(b);
System.out.println(c);

A 10\n10

B -10\n-10

C -10\n10

D 10\n-10

💡 Hint

Unary minus changes the sign, unary plus returns the value as is.

Variable b is assigned -a, so b is -10. Variable c is +b, which keeps the value -10. So both print -10.

❓ Predict Output

advanced

Output with mixed unary operators and expressions

What will be printed by this Java code?

Java

int x = 3;
int y = x++ + ++x + --x + x--;
System.out.println(y);

A 13

B 15

C 16

D 12

💡 Hint

Evaluate each part step-by-step, tracking x's value changes carefully.

Step by step: Initial x=3 - x++ returns 3, x becomes 4 - ++x increments to 5, returns 5 - --x decrements to 4, returns 4 - x-- returns 4, x becomes 3 Sum: 3 + 5 + 4 + 4 = 16

❓ Predict Output

advanced

Output of unary logical complement operator

What is the output of this Java code?

Java

boolean flag = false;
System.out.println(!flag);
System.out.println(!!flag);

A false\ntrue

B true\ntrue

C false\nfalse

D true\nfalse

💡 Hint

The ! operator flips the boolean value.

First print: !false is true. Second print: !!false is !(!false) which is !true = false.

🧠 Conceptual

expert

Effect of unary operators on variable values

Given the following Java code, what is the final value of variable 'a' after execution?

Java

int a = 1;
int b = a++ + ++a + a-- + --a;

A 1

B 4

C 3

D 2

💡 Hint

Track the value of 'a' carefully after each unary operation.

Initial a=1 Evaluate b: a++ returns 1, a=2 ++a increments a to 3, returns 3 a-- returns 3, a=2 --a decrements a to 1, returns 1 Sum for b: 1+3+3+1=8 (not asked) Final a after all operations is 1.