Re: Can a method be a parameter of another method in Java?

From:
AndrewMcDonagh <newsamd@amc.com>
Newsgroups:
comp.lang.java.programmer
Date:
Wed, 13 Sep 2006 20:17:34 +0100
Message-ID:
<ee9lgv$r8s$2@news.freedom2surf.net>
Shawn wrote:

Shawn wrote:

Hi,

Could you provide me one more example to achieve the following effect
in Java? Thank you very much.

var a = [1,2,3];
        for (i=0; i<a.length; i++)
    {
        a[i] = a[i] * 2;
    }
        for (i=0; i<a.length; i++)
    {
        alert(a[i]);
    }
Doing something to every element of an array is pretty common, and you
can write a function that does it for you:

    function map(fn, a)
    {
        for (i = 0; i < a.length; i++)
        {
            a[i] = fn(a[i]);
        }
    }
Now you can rewrite the code above as:

    map( function(x){return x*2;}, a );
    map( alert, a );


I tried the following file Test.java. It didn't work.

/*
For testing passing a method as a method parameter
*/

interface Mapper {
  void map(int[] d);
}

class Test {

        void doSomethingToArray(Mapper m, int[] aArray) {
                m.map(aArray);
        } //end of method doSomethingToArray

        Mapper squareArray = new Mapper() {
                void map(int[] a)
                {
                        for (int i=0; i<a.length; i++)
                        {
                                a[i] *= a[i];
                        }
                }
        }

        Mapper printArray = new Mapper() {
                void map(int[] a)
                {
                        for (int i=0; i<a.length; i++)
                        {
                                System.out.println(a[i]);
                        }
                }

          } ;

you are missing a ';' on the '}' above

        static int[] a={2, 4, 6, 8};

        public static void main(String[] args)
        {
                doSomethingToArray(squareArray, a);
                doSomethingToArray(printArray, a);
        }

} //end of class Test

Below is the error message. I cannot solve it. Back to the interface
issue, I am not allowed to instantiate an interface even I implement its
method?

Thank you very much for your help.

 >javac Test.java
----------
1. ERROR in Test.java (at line 25)
        Mapper printArray = new Mapper() {
        ^^^^^^
Syntax error on token "Mapper", ";", "," expected
----------
2. ERROR in Test.java (at line 39)
        doSomethingToArray(squareArray, a);
                           ^^^^^^^^^^^
Cannot make a static reference to the non-static field squareArray
----------
3. ERROR in Test.java (at line 40)
        doSomethingToArray(printArray, a);
                           ^^^^^^^^^^
Cannot make a static reference to the non-static field printArray
----------
3 problems (3 errors)

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