If

On its own, an if statement lets the program decide whether or not to run a block of code. This means the code inside the if block can be skipped. For example:

println("Please enter a number less than 100.");
int number = nextInt();

if (number < 100) {
    println("Thanks for following directions!");
}

This program only prints its second message if the user types a number less than 100. If the user types a number greater than or equal to 100, then the program will skip the second print statement.

An if statement has several parts:

• The if keyword
• A condition in parenthesis after the if, which is always a boolean expression
• An opening curly brace ({) to begin a code block; this code block and its contents are the body of the if statement
• Some code indented within the code block
• A closing curly brace (}) to end the code block

When an if statement is executed, the condition is first evaluated. This will result in either true or false. If the condition is true, then the body of the if statement will execute. If the condition is false, then the program skips the body and continues executing the rest of the program.

Semicolons

Note that we do not include a semicolon on the lines with curly braces. Java expects that a statement, as in a line of code that represents a complete instruction, will always end in a semicolon. The if (condition) { line is not an instruction on its own, so we should not place a semicolon on that line. In general, any time you write a line of code that would normally be followed by an opening curly brace (such as an if), you should not use a semicolon on that line.