74 lines
2.3 KiB
Java
74 lines
2.3 KiB
Java
import java.lang.reflect.*;
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/**
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* This program demonstrates the use of reflection for manipulating arrays.
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* @version 1.01 2004-02-21
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* @author Cay Horstmann
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*/
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public class ArrayGrowTest
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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[]) goodArrayGrow(a);
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arrayPrint(a);
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String[] b = { "Tom", "Dick", "Harry" };
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b = (String[]) goodArrayGrow(b);
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arrayPrint(b);
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System.out.println("The following call will generate an exception.");
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b = (String[]) badArrayGrow(b);
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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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* @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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static Object[] badArrayGrow(Object[] a)
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{
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int newLength = a.length * 11 / 10 + 10;
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Object[] newArray = new Object[newLength];
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System.arraycopy(a, 0, newArray, 0, a.length);
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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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static Object goodArrayGrow(Object a)
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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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int newLength = length * 11 / 10 + 10;
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Object newArray = Array.newInstance(componentType, newLength);
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System.arraycopy(a, 0, newArray, 0, length);
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return newArray;
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}
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/**
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* A convenience method to print all elements in an array
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* @param a the array to print. It can be an object array or a primitive type array
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*/
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static void arrayPrint(Object a)
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{
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Class cl = a.getClass();
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if (!cl.isArray()) return;
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Class componentType = cl.getComponentType();
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int length = Array.getLength(a);
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System.out.print(componentType.getName() + "[" + length + "] = { ");
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for (int i = 0; i < Array.getLength(a); i++)
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System.out.print(Array.get(a, i) + " ");
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System.out.println("}");
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}
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}
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