Java反射

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反射

一，反射就是加载类，并解剖出类的各个组成部分。一个类有多个组成部分，如：成员变量（filed），方法（method），构造方法（constructor）组成。

二，反射分为两个步骤，（一）加载类，（二），解剖出类的各个组成部分。
（一）加载类，获得类的字节码。
1,通过Class的forName方法获得类的字节码
Class clazz = Class.forName(“cn.cyy.reflect.Person”);
2.通过new对象，再调用对象的getClass方法得到字节码
Class clazz1 = new Person().getClass();
3.直接把类的字节码赋值给Class
Class clazz2 = Person.class;

package cn.cyy.reflect;public class Demo1 {    /**     * 反射：加载类，获得类的字节码     * @param args     * @throws ClassNotFoundException      */    public static void main(String[] args) throws ClassNotFoundException {        //1,通过Class的forName方法获得类的字节码        Class clazz = Class.forName("cn.cyy.reflect.Person");        //2.通过new对象，再调用对象的getClass方法得到字节码        Class clazz1 = new Person().getClass();        //3.直接把类的字节码赋值给Class        Class clazz2 = Person.class;    }}

二，反射出类的构造函数，字段，方法
1，反射出类构造方法

package cn.cyy.reflect;import java.lang.reflect.Constructor;import java.lang.reflect.Method;import java.util.ArrayList;import java.util.List;import org.junit.Test;/** * 反射类的构造函数，创建对象 * @author Administrator * */public class Demo2 {    //反射构造函数：public Person()    @Test    public void test1() throws Exception{        Class clazz = Class.forName("cn.cyy.reflect.Person");        Constructor c = clazz.getConstructor(null);        Object o = c.newInstance(null);        Method m = clazz.getMethod("getName",null);        System.out.println(m.invoke(o, null));    }    //public Person(String name)    @Test    public void test2() throws Exception{        Class clazz = Class.forName("cn.cyy.reflect.Person");        Constructor c = clazz.getConstructor(String.class);        Object obj = c.newInstance("yuli@cyy");        Method m = clazz.getMethod("getName",null);        System.out.println(m.invoke(obj, null));    }    //反射：public Person(String name,int password)    @Test    public void test3() throws Exception{        Class clazz = Class.forName("cn.cyy.reflect.Person");        Constructor c = clazz.getConstructor(String.class,int.class);        Object obj = c.newInstance("yuli",18);        Method m = clazz.getMethod("getName",null);        System.out.println(m.invoke(obj, null));    }    //反射：private Person(List list)    @Test    public void test4() throws Exception{        Class clazz = Class.forName("cn.cyy.reflect.Person");        Constructor c = clazz.getDeclaredConstructor(List.class);        c.setAccessible(true);        Object obj = c.newInstance(new ArrayList());        Method m = clazz.getMethod("getName",null);        System.out.println(m.invoke(obj, null));    }}

person类

package cn.cyy.reflect;import java.io.InputStream;import java.util.List;public class Person {    private String name = "cyy";    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public Person(){        System.out.println("person");    }    public Person(String name){        System.out.println("person "+name);    }    public Person(String name,int password){        System.out.println(name+":"+password);    }    private Person(List list){        System.out.println("list"+list);    }    public void testRft(){        System.out.println("testRft");    }    public void testRft(String name,int password){        System.out.println(name+":"+password);    }    public Class[] testRft(String name,int[] password){        return new Class[]{String.class};    }    private void testRft(InputStream in){        System.out.println(in);    }    public static void testRft(int num){        System.out.println(num);    }    public static void main(String []args){        System.out.println("main");        for (String str : args) {            System.out.println(str);        }    }}

2，反射出类的方法

package cn.cyy.reflect;import java.io.FileInputStream;import java.io.InputStream;import java.lang.reflect.Method;import org.junit.Test;//反射类的方法public class Demo3 {    //反射类的方法：public void testRft()    @Test    public void test1() throws Exception{        Class clazz = Class.forName("cn.cyy.reflect.Person");        Object obj = clazz.newInstance();        Method method = clazz.getMethod("testRft", null);        method.invoke(obj, null);    }    //反射类的方法：public void testRft(String name,int password)    @Test    public void test2() throws Exception{        Class clazz = Class.forName("cn.cyy.reflect.Person");        Object obj = clazz.newInstance();        Method method = clazz.getMethod("testRft", String.class,int.class);        method.invoke(obj, "cyy",24);    }    //反射类带有复杂参数的方法：public Class[] testRft(String name,int[] password)    @Test    public void test3() throws Exception{        Class clazz = Class.forName("cn.cyy.reflect.Person");        Object obj = clazz.newInstance();        Method method = clazz.getMethod("testRft", String.class,int[].class);        Class[] cl = (Class[]) method.invoke(obj, "cyy&yuli",new int[]{1,2,3});        System.out.println(cl[0]);    }    //反射类的私有方法：private void testRft(InputStream in)    @Test    public void test4() throws Exception{        Class clazz = Class.forName("cn.cyy.reflect.Person");        Object obj = clazz.newInstance();        Method method = clazz.getDeclaredMethod("testRft", InputStream.class);        method.setAccessible(true);        method.invoke(obj, new FileInputStream("c:\\log_network.txt"));    }    //反射类的静态方法：public static void testRft(int num)    @Test    public void test5() throws Exception{        Class clazz = Class.forName("cn.cyy.reflect.Person");        Method method = clazz.getMethod("testRft", int.class);        method.invoke(null, 23);    }    //反射类的main方法：public static void main(String []args)    @Test    public void test6() throws Exception{        Class clazz = Class.forName("cn.cyy.reflect.Person");        Method method = clazz.getMethod("main", String[].class);        method.invoke(null, new Object[]{new String[]{"1","23","456"}});    }}

3，反射类的字段

package cn.cyy.reflect;import java.lang.reflect.Field;import org.junit.Test;public class Demo4 {    //反射私有字段：private String name = "cyy";    @Test    public void test1() throws Exception{        Class clazz = Class.forName("cn.cyy.reflect.Person");        Object obj = clazz.newInstance();//加载类创建对象        Field f = clazz.getDeclaredField("name");//得到name字段        Class type = f.getType();//得到name字段的类型        f.setAccessible(true);//打开私有字段的访问权限        if(type.equals(String.class)){//如果字段是字符串，则赋值            f.set(obj, "yuli");//为字段name赋值            System.out.println(f.get(obj));//取出字段name的值        }    }    //反射公有字段：public int password = 123;    @Test    public void test2() throws Exception{        Class clazz = Class.forName("cn.cyy.reflect.Person");        Object obj = clazz.newInstance();//加载类创建对象        Field f = clazz.getField("password");        Class type = f.getType();        if(type.equals(int.class)){            f.set(obj, 567);            System.out.println(f.get(obj));        }    }    //反射类的静态字段：public static int age = 23;    @Test    public void test3() throws Exception{        Class clazz = Class.forName("cn.cyy.reflect.Person");        Object obj = clazz.newInstance();//加载类创建对象        Field f = clazz.getField("age");        Class type = f.getType();        if(type.equals(int.class)){            f.set(obj, 18);            System.out.println(f.get(obj));        }    }}

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