反射(获取构造器、方法)

反射

反射:
    1.获取class对象
        方式1:
            Class clazz=Class.forName("全限定名")
        方式2:
            Class clazz=类名.class;
        方式3:
            Class clazz=对象.getClass;
  

  2.可以获取对应类的构造方法(了解)
        Constructor con = clazz.getConstructor(Class .. paramClass);
        Person p = (Person) con.newInstance(参数);

　　 persion.java

package com.reflect;

public class Persion {
    private Integer id;
    private String username;
    private String password;
    
    public Persion() {
        System.out.println("无参构造器");
    }
    public Persion(Integer id, String username, String password) {
        this.id = id;
        this.username = username;
        this.password = password;
        System.out.println("带参构造器");
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }    
}

　　text01.java

package com.reflect;

import org.junit.Test;
import java.lang.reflect.*;

public class test01 {
    @Test
    public void run() throws Exception {
        //获取class对象
        Class clazz = Class.forName("com.reflect.Persion");
        
        //获取无参构造器
        Constructor con1  = clazz.getConstructor();
        Persion p1 = (Persion) con1.newInstance();    
        
        //获取带参构造器
        Constructor con2 = clazz.getConstructor(Integer.class,String.class,String.class);
        Persion p2 = (Persion) con2.newInstance(1,"hjh","12345");
    }
}

 3.可以通过clazz创建一个对象(了解)
        clazz.newInstance();//相当于调用的无参构造器
    4.可以通过clazz获取所有的字段 getFiled()(了解中的了解)

 5.可以通过clazz获取所有的方法
        Method m = clazz.getMethod("sleep");//获取公共的方法
        Method m = clazz.getDeclaredMethod("sleep");//获取任意的方法
        
        注意:若是私有的方法 必须让该方法可以访问
            m.setAccessible(true);

　　 persion.java

package com.reflect;

public class Persion {
    private Integer id;
    private String username;
    private String password;
    
    public Persion() {
        System.out.println("无参构造器");
    }
    public Persion(Integer id, String username, String password) {
        this.id = id;
        this.username = username;
        this.password = password;
        System.out.println("带参构造器");
    }
    public Persion( String username) {
        this.username = username;
    }
    
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    
    public void sport() {
        System.out.println("游泳");
    }
    public void sport(String username) {
        System.out.println(username+"在游泳");
    }
    private void sleep() {
        System.out.println("睡觉");
    }
    private String sleep(String username) {
        return username+"在睡觉";
    }
}

　　test02.java

package com.reflect;

import org.junit.Test;
import java.lang.reflect.*;

public class test02 {
    @Test
    public void run() throws Exception {
        //获取class对象
        Class clazz = Persion.class;
        
        //获取public修饰的方法
        Method m1 = clazz.getMethod("sport");
        m1.invoke(clazz.newInstance());
        
        //获取任意方法
        Method m2 = clazz.getDeclaredMethod("sleep");
        //授权给私有和受保护方法，使之可以被访问
        m2.setAccessible(true);
        //执行方法
        m2.invoke(clazz.newInstance());
        
        //执行有返回值的方法    
        Method m3 = clazz.getDeclaredMethod("sleep",String.class);
        //授权给私有和受保护方法，使之可以被访问
        m3.setAccessible(true);
        String str = (String) m3.invoke(clazz.newInstance(),"hjh");
        System.out.println(str);
    }
}

6.Method对象的invoke是有返回值,他的返回值就是目标方法执行的返回值
总结:
    有了class对象之后,无所不能.