59 lines
1.8 KiB
Java
59 lines
1.8 KiB
Java
package arrays;
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import java.lang.reflect.*;
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import java.util.*;
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/**
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* This program demonstrates the use of reflection for manipulating arrays.
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* @version 1.2 2012-05-04
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* @author Cay Horstmann
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*/
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public class CopyOfTest
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{
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public static void main(String[] args)
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{
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int[] a = { 1, 2, 3 };
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a = (int[]) goodCopyOf(a, 10);
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System.out.println(Arrays.toString(a));
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String[] b = { "Tom", "Dick", "Harry" };
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b = (String[]) goodCopyOf(b, 10);
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System.out.println(Arrays.toString(b));
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System.out.println("The following call will generate an exception.");
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b = (String[]) badCopyOf(b, 10);
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}
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/**
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* This method attempts to grow an array by allocating a new array and copying all elements.
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* @param a the array to grow
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* @param newLength the new length
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* @return a larger array that contains all elements of a. However, the returned array has
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* type Object[], not the same type as a
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*/
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public static Object[] badCopyOf(Object[] a, int newLength) // not useful
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{
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Object[] newArray = new Object[newLength];
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System.arraycopy(a, 0, newArray, 0, Math.min(a.length, newLength));
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return newArray;
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}
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/**
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* This method grows an array by allocating a new array of the same type and
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* copying all elements.
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* @param a the array to grow. This can be an object array or a primitive
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* type array
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* @return a larger array that contains all elements of a.
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*/
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public static Object goodCopyOf(Object a, int newLength)
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{
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Class cl = a.getClass();
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if (!cl.isArray()) return null;
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Class componentType = cl.getComponentType();
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int length = Array.getLength(a);
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Object newArray = Array.newInstance(componentType, newLength);
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System.arraycopy(a, 0, newArray, 0, Math.min(length, newLength));
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return newArray;
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}
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}
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