java反射

通过反射，可以设置一个类的field的值，或者调用一个类的方法，或者新生成这个类的实例。

测试代码：

package com.reflect;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import junit.framework.TestCase;

public class TestReflect extends TestCase {

	public void testMethod() {
		try {
			Method method = User.class.getDeclaredMethod("setAge", new Class[]{int.class});
			User user = new User();
			System.out.println(user);
			method.invoke(user, 18);
			System.out.println(user);
		} catch (SecurityException e) {
			e.printStackTrace();
		} catch (NoSuchMethodException e) {
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			e.printStackTrace();
		}
	}
	
	public void testField() {
		try {
			Field field = User.class.getDeclaredField("name");
			User user = new User();
			System.out.println(user);
			if (!field.isAccessible()) {
				field.setAccessible(true);
			}
			field.set(user, "yang");
			System.out.println(user);
		} catch (SecurityException e) {
			e.printStackTrace();
		} catch (NoSuchFieldException e) {
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		}
	}
	
	public void testConstructor1() {
		try {
			Constructor<?> con = User.class.getDeclaredConstructor((Class[])null);
			User user = (User)con.newInstance((Object[])null);
			System.out.println(user);
		} catch (SecurityException e) {
			e.printStackTrace();
		} catch (NoSuchMethodException e) {
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			e.printStackTrace();
		} catch (InstantiationException e) {
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			e.printStackTrace();
		}
	}
	
	public void testConstructor2() {
		try {
			Constructor<?> con = User.class.getDeclaredConstructor(new Class[]{int.class, String.class});
			User user = (User)con.newInstance(20, "yang");
			System.out.println(user);
		} catch (SecurityException e) {
			e.printStackTrace();
		} catch (NoSuchMethodException e) {
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			e.printStackTrace();
		} catch (InstantiationException e) {
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			e.printStackTrace();
		}
	}

	static class User {
		private int age;
		private String name;

		public User() {
		}

		public User(int age, String name) {
			this.age = age;
			this.name = name;
		}

		public int getAge() {
			return age;
		}

		public void setAge(int age) {
			this.age = age;
		}

		public String getName() {
			return name;
		}

		public void setName(String name) {
			this.name = name;
		}

		@Override
		public String toString() {
			return "User [age=" + age + ", name=" + name + "]";
		}
	}
}