The JavaTM Tutorial

| Start of Tutorial > Start of Trail > Start of Lesson | Search Feedback Form

Trail: The Reflection API
Lesson: Working with Arrays

## Creating Arrays

> If you are writing a development tool such as an application builder, you may want to allow the end user to create arrays at runtime. Your program can provide this capability by invoking the `Array.newInstance` method.

> The following sample program uses the `newInstance` method to create a copy of an array that is twice the size of the original array. The `newInstance` method accepts as arguments the length and component type of the new array. The source code follows:

> >     import java.lang.reflect.*;

> >     class SampleCreateArray {

> >        public static void main(String[] args) {
> >           int[] originalArray =  {55, 66};
> >           int[] biggerArray = (int[]) doubleArray(originalArray);
> >           System.out.println("originalArray:");
> >           for (int k = 0; k < Array.getLength(originalArray); k++)
> >              System.out.println(originalArray[k]);
> >           System.out.println("biggerArray:");
> >           for (int k = 0; k < Array.getLength(biggerArray); k++)
> >              System.out.println(biggerArray[k]);
> >        }

> >        static Object doubleArray(Object source) {
> >           int sourceLength = Array.getLength(source);
> >           Class arrayClass = source.getClass();
> >           Class componentClass = arrayClass.getComponentType();
> >           Object result = Array.newInstance(componentClass,
> >                                             sourceLength * 2);
> >           System.arraycopy(source, 0, result, 0, sourceLength);
> >           return result;
> >        }
> >     }

> The output of the preceding program is:

> >     originalArray:
> >     55
> >     66
> >     biggerArray:
> >     55
> >     66
> >     0
> >     0

> You can also use the `newInstance` method to create multidimensional arrays. In this case, the parameters of the method are the component type and an array of `int` types representing the dimensions of the new array.

> The next sample program shows how to use `newInstance` to create multidimensional arrays:

> >     import java.lang.reflect.*;

> >     class SampleMultiArray {

> >        public static void main(String[] args) {

> >           // The oneDimA and oneDimB objects are one
> >           // dimensional int arrays with 5 elements.

> >           int[] dim1 = {5};
> >           int[] oneDimA = (int[]) Array.newInstance(int.class, dim1);
> >           int[] oneDimB = (int[]) Array.newInstance(int.class, 5);

> >           // The twoDimStr object is a 5 X 10 array of String objects.

> >           int[] dimStr = {5, 10};
> >           String[][] twoDimStr =
> >                      (String[][]) Array.newInstance(String.class,dimStr);

> >           // The twoDimA object is an array of 12 int arrays. The tail
> >           // dimension is not defined. It is equivalent to the array
> >           // created as follows:
> >           //    int[][] ints = new int[12][];

> >           int[] dimA = {12};
> >           int[][] twoDimA = (int[][]) Array.newInstance(int[].class, dimA);
> >        }
> >     }

| Start of Tutorial > Start of Trail > Start of Lesson | Search Feedback Form

Copyright 1995-2001 Sun Microsystems, Inc. All rights reserved.