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Summary of Control Flow Statements

For controlling the flow of a program, the Java programming language has three loop constructs, a flexible if-else statement, a switch statement, exception-handling statements, and branching statements.

Loops

Use the while statement to loop over a block of statements while a boolean expression remains true. The expression is evaluated at the top of the loop:

while (boolean expression) {
    statement(s)
}

Use the do-while statement to loop over a block of statements while a boolean expression remains true. The expression is evaluated at the bottom of the loop, so the statements within the do-while block execute at least once:

do {
    statement(s)
} while (expression);

The for statement loops over a block of statements and includes an initialization expression, a termination condition expression, and an increment expression:

for (initialization ; termination ; increment) {
    statement(s)
}

Decision-Making Statements

The Java programming language has two decision-making statements: if-else and switch. The more general-purpose statement is if; use switch to make multiple-choice decisions based on a single integer value.

The following is the most basic if statement whose single statement block is executed if the boolean expression is true:

if (boolean expression) {
    statement(s)
}

Here's an if statement with a companion else statement. The if statement executes the first block if the boolean expression is true; otherwise, it executes the second block:

if (boolean expression) {
    statement(s)
} else {
    statement(s)
}

You can use else if to construct compound if statements:

if (boolean expression) {
    statement(s)
} else if (boolean expression) {
    statement(s)
} else if (boolean expression) {
    statement(s)
} else {
    statement(s)
}

The switch statement evaluates an integer expression or enum and executes the appropriate case statement.

switch (integer expression) {
    case integer expression:
         statement(s)
         break;
    ...
    default:
         statement(s)
         break;
}

switch (expression of enum type) {
    case enum constant:
         statement(s)
         break;
    ...
    default:
         statement(s)
         break;
}

Exception-Handling Statements

Use the try, catch, and finally statements to handle exceptions:

try {
    statement(s)
} catch (exceptiontype name) {
    statement(s)
} catch (exceptiontype name) {
    statement(s)
} finally {
    statement(s)
}

Exception handling is covered in detail in the chapter Handling Errors with Exceptions.

Branching Statements

Some branching statements change the flow of control in a program to a labeled statement. You label a statement by placing a legal identifier (the label) followed by a colon (:) before the statement:

statementName: someJavaStatement;

Use the unlabeled form of the break statement to terminate the innermost switch, for, while, or do-while statement:

break;

Use the labeled form of the break statement to terminate an outer switch, for, while, or do-while statement with the given label:

break label;

A continue statement terminates the current iteration of the innermost loop and evaluates the boolean expression that controls the loop:

continue;

The labeled form of the continue statement skips the current iteration of the loop with the given label:

continue label;

Use return to terminate the current method:

return;

You can return a value to the method's caller, by using the form of return that takes a value:

return value;

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