Java Prefix vs. Postfix Increment/Decrement: Why Does `i ` Result in 7 in This Example?

Prefix and Postfix Increment/Decrement Operators in Java

Understanding the difference between prefix and postfix increment/decrement operators is crucial in Java programming. This article explores the effects of these operators in a practical example.

Question:

Consider the following code snippet:

int i = 3;
i++; // Postfix increment

System.out.println(i);    // Prints "4"

++i; // Prefix increment
System.out.println(i);    // Prints "5"
System.out.println(++i);  // Prints "6"
System.out.println(i++);  // Prints "6"
System.out.println(i);    // Prints "7"

Why does the last call to System.out.println(i) print the value 7?

Answer:

The behavior of this code is governed by the semantics of prefix and postfix increment operators:

• Prefix increment ( ): Increments the operand before it is used in an expression.
• Postfix increment ( ): Increments the operand after it has been used in an expression.

Prefix Increment:

int i = 6;
System.out.println(++i); // Prints "6"

i evaluates to 7, as it increments i before using its value in the expression. So it prints "6" and increments i to 7.

Postfix Increment:

int i = 6;
System.out.println(i++); // Prints "6" (i = 7, prints 6)

i evaluates to 6, as it stores a copy of i, adds 1 to i, and returns the original value. The expression prints "6", but i is now 7.

In the last call, System.out.println(i) prints the current value of i, which is 7. This is because the postfix increment operator had previously updated it to 7.

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