java反射详解

下面是java反射的两个例子

Reflection，通过一个类名，打印出构造函数，方法和变量

 

package com.zcb;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Scanner;
/**
 * 
 * @author zhengchubin
 *
 */
public class ReflectionTest {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		String name;
		if (args.length > 0)
			name = args[0];
		else {
			System.out.println("Enter class name (e.g. java.util.Date): ");
			Scanner in = new Scanner(System.in);
			name = in.nextLine();
		}
		try {
			Class cl = Class.forName(name);
			Class superClass = cl.getSuperclass();
			String modifiers = Modifier.toString(cl.getModifiers());
			if (modifiers.length() > 0)
				System.out.print(modifiers + " ");
			System.out.print("class " + name);
			if (superClass != null && superClass != Object.class)
				System.out.print("extends " + superClass.getName());
			System.out.print("\n{\n");
			printConstructors(cl);// 打印构造方法
			System.out.println();
			printMethods(cl);// 打印方法
			System.out.println();
			printFields(cl);// 打印数据成员
			System.out.println("}");

		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		System.exit(0);

	}

	private static void printFields(Class cl) {
		// TODO Auto-generated method stub
		Field[] fields = cl.getDeclaredFields();
		for (Field f : fields) {
			System.out.print("\t");
			Class type = f.getType();
			String name = f.getName();
			String modifiers = Modifier.toString(f.getModifiers());
			if (modifiers.length() > 0)
				System.out.print(modifiers + " ");
			System.out.println(type.getName() + " " + name + ";");
		}
	}

	private static void printMethods(Class cl) {
		// TODO Auto-generated method stub
		Method[] methods = cl.getDeclaredMethods();
		for (Method m : methods) {
			System.out.print("\t");
			Class retType = m.getReturnType();
			String name = m.getName();
			String modifiers = Modifier.toString(m.getModifiers());
			System.out.print(modifiers + " ");
			System.out.print(retType + " " + name + "(");
			@SuppressWarnings("rawtypes")
			Class[] paramTypes = m.getParameterTypes();
			for (int j = 0; j < paramTypes.length; j++) {
				if (j > 0)
					System.out.print(", ");
				System.out.print(paramTypes[j].getName());
			}
			System.out.println(");");
		}
	}

	private static void printConstructors(Class cl) {
		// TODO Auto-generated method stub
		@SuppressWarnings("rawtypes")
		Constructor[] constructors = cl.getDeclaredConstructors();
		for (Constructor c : constructors) {
			System.out.print("\t");
			String name = c.getName();
			String modifiers = Modifier.toString(c.getModifiers());
			System.out.print(modifiers + " ");
			System.out.print(name + "(");
			@SuppressWarnings("rawtypes")
			Class[] paramTypes = c.getParameterTypes();
			for (int j = 0; j < paramTypes.length; j++) {
				if (j > 0)
					System.out.print(", ");
				System.out.print(paramTypes[j].getName());
			}
			System.out.println(");");
		}
	}

}

运行结果：

MethodPointer相当于C/C++中的回调函数

package com.zcb;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
/**
 * 
 * @author zhengchubin
 *
 */
public class MethodPointerTest {

	public static void main(String[] args) throws SecurityException,
			NoSuchMethodException {
		// TODO Auto-generated method stub
		Method square = MethodPointerTest.class.getMethod("square",
				double.class);
		Method sqrt = Math.class.getMethod("sqrt", double.class);
		printTable(1, 10, 10, square);
		printTable(1, 10, 10, sqrt);
	}

	public static double square(double x) {
		return x * x;
	}

	private static void printTable(int i, int j, int k, Method f) {
		// TODO Auto-generated method stub
		double x = (j - i) / (k - 1);
		for (double l = i; l <= j; l += x) {
			double y;
			try {
				y = (Double) f.invoke(null, l);
				System.out.printf("%10.4f|%10.4f%n", l, y);
			} catch (IllegalArgumentException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (IllegalAccessException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (InvocationTargetException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}

		}
	}

}

运行结果：