Lesson 7: If Statement - Intro to Java

If Statement Only run code when a condition is true.

1public static void main(String[] args) {

2 boolean isTrue = true;

3 if (isTrue) {

4 System.out.println("isTrue is true");

5 }

Terminal

$ javac Main.java

$ java Main

isTrue is true

Every line, explained

public static void main(String[] args) {: Every Java program starts at the main method. When you run the program, Java looks for this exact line, public static void main(String[] args), and runs everything between its { and } from top to bottom.
boolean isTrue = true;: boolean declares a variable that can store only one of two values: true or false. Watch the spelling: in Java the type is boolean; writing bool (like some other languages use) will not compile.
if (isTrue) {: if checks the condition inside its parentheses. If the condition is true, Java runs the code between the { and }. If it is false, Java skips that code completely. Here the condition is simply the variable isTrue, which is true, so the code inside runs.
System.out.println("isTrue is true");: System.out.println(...) prints whatever is inside the parentheses to the terminal, then moves to a new line. Read the name carefully: print-l-n is short for "print line".
}: This } closes the if block.
}: This closing curly brace } ends the main method. In Java every opening brace { must have a matching closing brace }.