corejava第8版

corejava第8版/v1ch05/ArrayGrowTest/ArrayGrowTest.java

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+import java.lang.reflect.*;
+
+/**
+ * This program demonstrates the use of reflection for manipulating arrays.
+ * @version 1.01 2004-02-21
+ * @author Cay Horstmann
+ */
+public class ArrayGrowTest
+{
+   public static void main(String[] args)
+   {
+      int[] a = { 1, 2, 3 };
+      a = (int[]) goodArrayGrow(a);
+      arrayPrint(a);
+
+      String[] b = { "Tom", "Dick", "Harry" };
+      b = (String[]) goodArrayGrow(b);
+      arrayPrint(b);
+
+      System.out.println("The following call will generate an exception.");
+      b = (String[]) badArrayGrow(b);
+   }
+
+   /**
+    * This method attempts to grow an array by allocating a new array and copying all elements.
+    * @param a the array to grow
+    * @return a larger array that contains all elements of a. However, the returned array has 
+    * type Object[], not the same type as a
+    */
+   static Object[] badArrayGrow(Object[] a)
+   {
+      int newLength = a.length * 11 / 10 + 10;
+      Object[] newArray = new Object[newLength];
+      System.arraycopy(a, 0, newArray, 0, a.length);
+      return newArray;
+   }
+
+   /**
+    * This method grows an array by allocating a new array of the same type and
+    * copying all elements.
+    * @param a the array to grow. This can be an object array or a primitive
+    * type array
+    * @return a larger array that contains all elements of a.
+    */
+   static Object goodArrayGrow(Object a)
+   {
+      Class cl = a.getClass();
+      if (!cl.isArray()) return null;
+      Class componentType = cl.getComponentType();
+      int length = Array.getLength(a);
+      int newLength = length * 11 / 10 + 10;
+
+      Object newArray = Array.newInstance(componentType, newLength);
+      System.arraycopy(a, 0, newArray, 0, length);
+      return newArray;
+   }
+
+   /**
+    * A convenience method to print all elements in an array
+    * @param a the array to print. It can be an object array or a primitive type array
+    */
+   static void arrayPrint(Object a)
+   {
+      Class cl = a.getClass();
+      if (!cl.isArray()) return;
+      Class componentType = cl.getComponentType();
+      int length = Array.getLength(a);
+      System.out.print(componentType.getName() + "[" + length + "] = { ");
+      for (int i = 0; i < Array.getLength(a); i++)
+         System.out.print(Array.get(a, i) + " ");
+      System.out.println("}");
+   }
+}