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Re-writing the for-statement using a while-statement and vice versa

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• Relationship between the while-statement and the for-statement
  • The for-statement and the while-statement have many aspects in common

    They can often replace each other.

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  • Facts:

    A while-statement can always be re-written using a for-statement A for-statement that does not contain any continue-statement in its body, can be easily re-written using a while-statement. (A for-statement that does contain a continue-statement in its body, needs a bit more work to be re-written into a while-statement.)

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• Re-writing a while-statement using a for-statement
  • While-statement:

    can be written as follows using a for-statement:

    (We simply use an empty statement as the INIT-STATEMENT and as the INCR-STATEMENT)

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  • Example:

    While-statement	Equivalent for-statement
    a = 1; while ( a <= 10 ) { System.out.println(a); a++; }	a = 1; for ( ; a <= 10 ; ) { System.out.println(a); a++; }

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• Re-writing a for-statement using a while-statement
  • For-statement:

    that does not contain a continue-statement, can be written as follows using a while-statement:

    (We move the INIT-STATEMENT before the while-statement and put the INCR-STATEMENT as the last statement in the body)

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  • Example:

    For-statement	Equivalent while-statement
    for ( a = 1 ; a <= 10 ; a++ ) { System.out.println(a); }	a = 1; while ( a <= 10 ) { System.out.println(a); a++; }

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  • Note:

    A for-statement that executes a continue-statement will jump to the INCR-STATEMENT On the other hand, a while-statement that executes a continue-statement will jump to the end and continues with testing the loop-continuation-condition Thus: to replace a for-statement containing a continue-statement with a while-loop, each continue statement must be re-written using: in for-statement in while-statement ------------------- -------------------- continue; INCREMENT; // (from the for-loop) continue;

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• Abusing the Java for-statement
  • If a for-statement does not contain any continue statements, you can re-write the for-statement as follows:

    Example:

    Original for-statement	Abused for-statement
    for ( a = 1 ; a <= 10 ; a++ ) { System.out.println(a); }	a = 1; for ( ; a <= 10 ; ) { System.out.println(a); a++; }

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  • Example Program: (Shows the abused for-loop)                                                
    • Prog file: click here

    How to run the program:

    Right click on link and save in a scratch directory To compile:   javac For02.java To run:          java For02