Java: if Statement - Overview

Purpose

The purpose of the if statement is to make decisions, and execute different parts of your program depending on a boolean true/false value. About 99% of the flow decisions are made with if. [The other 1% of the decisions use the switch/case statement.]

General Forms

The if statement has this form:

do these statements
if (condition) {
    do this clause if the condition is true
}
do these statements afterwards

or

do these statements
if (condition) {
    do this clause if the condition is true
} else {
    do this clause if the condition is false
}
do these statements afterwards

It is good programming style to always write the curly braces, {}, altho they are not needed if the clause contains only a single statement.

Condition is true or false

The value of condition must be true or false (ie, a boolean value). It is often a comparison.

. . .
if (marks < 60) {
    JOptionPane.showMessageDialog(null, "This is terrible");
} else {
    JOptionPane.showMessageDialog(null, "Not so bad");
}
. . .

The code above will display one of two dialogs, depending on teh value of marks.