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For controlling the flow of a program, the Java programming language has three loop constructs, a flexibleif-elsestatement, aswitchstatement, exception-handling statements, and branching statements.
Use thewhilestatement to loop over a block of statements while a boolean expression remainstrue. The expression is evaluated at the top of the loop.while (boolean expression) { statement(s) }Use the
do-whilestatement to loop over a block of statements while a boolean expression remainstrue. The expression is evaluated at the bottom of the loop, so the statements within thedo-whileblock execute at least once:do { statement(s) } while (expression);The
forstatement 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) }
The Java programming language has two decision-making statements:if-elseandswitch. The more general-purpose statement isif; useswitchto make multiple-choice decisions based on a single integer value. The following is the most basicifstatement whose single statement block is executed if the boolean expression istrue:Here's anif (boolean expression) { statement(s) }ifstatement with a companionelsestatement. Theifstatement executes the first block if the boolean expression istrue; otherwise, it executes the second block:You can useif (boolean expression) { statement(s) } else { statement(s) }else ifto construct compoundifstatements:Theif (boolean expression) { statement(s) } else if (boolean expression) { statement(s) } else if (boolean expression) { statement(s) } else { statement(s) }switchstatement evaluates an integer expression and executes the appropriatecasestatement.switch (integer expression) { case integer expression: statement(s) break; ... default: statement(s) break; }
Use thetry,catch, andfinallystatements to handle exceptions.try { statement(s) } catch (exceptiontype name) { statement(s) } catch (exceptiontype name) { statement(s) } finally { statement(s) }
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:Use the unlabeled form of thestatementName: someJavaStatement;breakstatement to terminate the innermostswitch,for,while, ordo-whilestatement.Use the labeled form of thebreak;breakstatement to terminate an outerswitch,for,while, ordo-whilestatement with the given label:Abreak label;continuestatement terminates the current iteration of the innermost loop and evaluates the boolean expression that controls the loop.The labeled form of thecontinue;continuestatement terminates the current iteration of the loop with the given label:Usecontinue label;returnto terminate the current method.You can return a value to the method's caller, by using the form ofreturn;returnthat takes a value.return value;
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