corejava第8版

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

@@ -0,0 +1,59 @@
+import java.lang.reflect.*;
+
+/**
+ * This program shows how to invoke methods through reflection.
+ * @version 1.1 2004-02-21
+ * @author Cay Horstmann
+ */
+public class MethodPointerTest
+{
+   public static void main(String[] args) throws Exception
+   {
+      // get method pointers to the square and sqrt methods
+      Method square = MethodPointerTest.class.getMethod("square", double.class);
+      Method sqrt = Math.class.getMethod("sqrt", double.class);
+
+      // print tables of x- and y-values
+
+      printTable(1, 10, 10, square);
+      printTable(1, 10, 10, sqrt);
+   }
+
+   /**
+    * Returns the square of a number
+    * @param x a number
+    * @return x squared
+    */
+   public static double square(double x)
+   {
+      return x * x;
+   }
+
+   /**
+    * Prints a table with x- and y-values for a method
+    * @param from the lower bound for the x-values
+    * @param to the upper bound for the x-values
+    * @param n the number of rows in the table
+    * @param f a method with a double parameter and double return value
+    */
+   public static void printTable(double from, double to, int n, Method f)
+   {
+      // print out the method as table header
+      System.out.println(f);
+
+      double dx = (to - from) / (n - 1);
+
+      for (double x = from; x <= to; x += dx)
+      {
+         try
+         {
+            double y = (Double) f.invoke(null, x);
+            System.out.printf("%10.4f | %10.4f%n", x, y);
+         }
+         catch (Exception e)
+         {
+            e.printStackTrace();
+         }
+      }
+   }
+}