The if-then statement is the most simple control flow we can write. It tests an expression for truth and executes some code based on it.

if (flip == 1) {

  System.out.println("Heads!");

}

• The if keyword marks the beginning of the conditional statement, followed by parentheses ().
• The parentheses hold a boolean datatype.

For the condition in parentheses we can also use variables that reference a boolean, or comparisons that evaluate to a boolean.

The boolean condition is followed by opening and closing curly braces that mark a block of code. This block runs if, and only if, the boolean is true.

boolean isValidPassword = true;

if (isValidPassword) {

  System.out.println("Password accepted!");

}

// Prints "Password accepted!"

int numberOfItemsInCart = 9;

if (numberOfItemsInCart > 12) {

  System.out.println("Express checkout not available");

}

// Nothing is printed.

If a conditional is brief we can omit the curly braces entirely:

if (true) System.out.println("Brevity is the soul of wit");

Note: Conditional statements do not end in a semicolon.