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Effect of the break and continue statements on the for-statement

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• Previously discussed...
  • The break statement

    When the break statement is executed inside a loop-statement, the loop-statement is terminated immediately The execution of the program will continue with the statement following the loop-statement

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  • The continue statement

    When the continue statement is executed inside a loop-statement, the program will skip over the remainder of the loop-body to the end of the loop body

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• Effect of the break-statement on a for-statement
  • According to:

    When the break statement is executed inside a loop-statement, the loop-statement is terminated immediately The execution of the program will continue with the statement following the loop-statement

    the effect is:

    The for-statement is terminated Execution continues with the statement that follows the for-statement

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  • The excution of the break statement illustrated with a flow chart:

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• Effect of the continue-statement on a for-statement
  • According to:

    When the continue statement is executed inside a loop-statement, the program will skip over the remainder of the loop-body to the end of the loop body

    the effect is:

    The for-statement skips over the rest of the body... ... because the INCR-STATEMENT is the next statement... Execution continues with the INCR-STATEMENT and then back to the LOOP-CONTINUATION-CONDITION

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  • The excution of the continue statement illustrated with a flow chart:

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• Caveat in using the continue-statement
  • Warning:

    The continue-statement can cause an infinite loop when used inside a while-statement

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  • Example: print all number 1, 2, ..., 10, except the number 4

    public class Continue02 { public static void main(String[] args) { int a; a = 1; while ( a <= 10 ) // Run a = 1, 2, ..., 10 { if ( a == 4 ) { continue; // Skip printing 4... } System.out.println(a); // Print a a++; } } }

    This program contains an infinite loop, because the continue statement will skip over a++.

    Result:

    When a == 4, the variable a is not increased inside the while-body !!!

    Since variable a does not change, you have an infinite loop

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  • Example Program: (Demo above code)                                                
    • Prog file: click here

    How to run the program:

    Right click on link and save in a scratch directory To compile:   javac Continue02.java To run:          java Continue02

    Output:

    1 2 3 (program hangs here forever)......

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  • On the other hand, a continue statement inside a for-statement will not create an infinite loop:

    public class Continue03 { public static void main(String[] args) { int a; for ( a = 1; a <= 10 ; a++ ) // Run a = 1, 2, ..., 10 { if ( a == 4 ) { continue; // Skip printing 4... } System.out.println(a); // Print a } } }

    Output of this program:

    1 2 3 (skips over 4 !) 5 6 7 8 9 10

    Reason:

    The continue statement will cause the exeution to jump to the INCR-STATEMENT (a++) The variable a is increased... So no infinite loop

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  • Example Program: (Demo above code)                                                
    • Prog file: click here

    How to run the program:

    Right click on link and save in a scratch directory To compile:   javac Continue03.java To run:          java Continue03