java reflect反射

TestClass类

package Reflect;

public class TestClass {
    public TestClass(){}
    public TestClass(int i){
        this.iTest = i;
    }
    
    private int iTest = 100;

    public int getiTest() {
        return iTest;
    }

    public void setiTest(int iTest) {
        this.iTest = iTest;
    }
}

 1.获得class name的三种方法

package Reflect;

public class Main {
    public static void main(String []args) {
        Class<?> c1 = null;
        Class<?> c2 = null;
        Class<?> c3 = null;
        
        try {
            c1 = Class.forName("Reflect.TestClass");
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        c2 = new TestClass().getClass();
        c3 = TestClass.class;
        
        System.out.println("C1="+c1.getName());//输出C1=Reflect.TestClass
        System.out.println("C2="+c2.getName());//输出C2=Reflect.TestClass
        System.out.println("C3="+c3.getName());//输出C3=Reflect.TestClass
        
    }
}

2.通过Class.NewInstance()创建新的类示例

package Reflect;

public class Main {
    public static void main(String []args) {
        Class<?> c1 = null;
        
        try {
            c1 = Class.forName("Reflect.TestClass");//要点1:这里只是对类的加载和连接
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        TestClass tc = null;
        try {
            tc = (TestClass) c1.newInstance();//要点2:到这里才是类的实例化,之前只是加载和连接；要点3:newInstance调用的是非私有的无参构造函数
        } catch (InstantiationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        System.out.println(tc.getiTest());        
    }
}

3.通过Constructor.newInstance()创建新的类示例

将TestClass里添加带参数的构造函数并设置为私有

    private TestClass(int i){
        this.iTest = i;
    }
    
    private TestClass(int i,int useless){
        this.iTest = i;
    }

package Reflect;

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

public class Main {
    public static void main(String []args) throws NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
        Class<?> c1 = null;
        
        try {
            c1 = Class.forName("Reflect.TestClass");//要点1:这里只是对类的加载和连接
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        Constructor<?> cc0 = c1.getDeclaredConstructor();
        cc0.setAccessible(true);
        TestClass tcc0 = (TestClass)cc0.newInstance();
        System.out.println(tcc0.getiTest());        
        //调用私有的构造函数
        Constructor<?> cc1 = c1.getDeclaredConstructor(int.class);
        cc1.setAccessible(true);
        TestClass tcc1 = (TestClass)cc1.newInstance(10);
        System.out.println(tcc1.getiTest());
        
        //调用私有的多参数构造函数
        Constructor<?> cc2 = c1.getDeclaredConstructor(int.class,int.class);
        cc2.setAccessible(true);
        TestClass tcc2 = (TestClass)cc2.newInstance(20,0);
        System.out.println(tcc2.getiTest());
    }
}

4.修改私有函数和私有变量

将setiTest设置为私有

    private void setiTest(int iTest) {
        this.iTest = iTest;
    }

package Reflect;

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

public class Main {
    public static void main(String []args) {
        Class<TestClass> clazz = TestClass.class;
        TestClass tc;
        try {
            tc = clazz.newInstance();            
            //调用私有方法
            Method method = clazz.getDeclaredMethod("setiTest", int.class);//函数名,参数/参数数组
            method.setAccessible(true);//设置不进行访问检查
            method.invoke(tc, 123);            //实例, 参数值
            System.out.println(tc.getiTest());    
            
            //修改私有变量的值
            Field field = clazz.getDeclaredField("iTest");//变量名
            field.setAccessible(true);//设置不进行访问检查
            field.set(tc, 12345);//实例,要修改的值
            System.out.println(tc.getiTest());
        } catch (InstantiationException | IllegalAccessException | NoSuchMethodException | SecurityException | IllegalArgumentException | InvocationTargetException | NoSuchFieldException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }        
    }
}