java反射温习一下

public class LoveReflect {
    public static class Demo  implements Serializable{
        
    }
    
    public static void main(String[] arg) {
        Demo demo = new Demo();
        System.out.println(demo.getClass().getName());
    }
}

输出

LoveReflect$Demo
ERROR: JDWP Unable to get JNI 1.2 environment, jvm->GetEnv() return code = -2
JDWP exit error AGENT_ERROR_NO_JNI_ENV(183): [../../../src/share/back/util.c:820]

import java.io.Serializable;
import java.lang.reflect.Array;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.HashMap;
import java.util.Map;

public class LoveReflect {
    public static class SubClass implements Serializable {
        private int id;
        private String name;

        public SubClass() {
        }

        public SubClass(Integer id, String name) {
            this.id = id;
            this.name = name;
        }

        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }
        
        public void subMethod() {
            System.out.println("hello world");
        }
    }

    public static void main(String[] arg) {
        SubClass subClass = new SubClass();

        //【案例1】通过名字取得类的声明，再取得名字
        System.out.println(subClass.getClass().getName());
        
        Class<?> demo1;
        try {
            //【案例2】通过名字取得类的声明
            demo1 = Class.forName("LoveReflect$SubClass");
            System.out.println(demo1.getName());

            //【案例3】通过名字找到类的声明，再创建实例
            SubClass subClass2 = (SubClass) Class.forName("LoveReflect$SubClass").newInstance();
            subClass2.setId(1);
            subClass2.setName("aaaa");
            System.out.println(subClass2.getName());

            //【案例4】拿类的的构造函数new实例
            Class<?>[] parameterTypes = {Integer.class,String.class};
            Constructor constructor = Class.forName("LoveReflect$SubClass").getDeclaredConstructor(parameterTypes);
            SubClass subClass3 = (SubClass)constructor.newInstance(2,"222222222222222222");
            System.out.println(subClass3.getName());
            
//            改个属性值
            Field f = subClass3.getClass().getDeclaredField("name");
            Class<?> type = f.getType();
            System.out.println("field type="+type.getName());
            int mod = f.getModifiers();
            System.out.println("modify="+Modifier.toString(mod));
            
            f.setAccessible(true);
            f.set(subClass3, "bbbbbbbbbbbbbbb");
            System.out.println(subClass3.getName());
            
            Map<Integer,Method> methods = new HashMap<Integer,Method>();
            Class<?>[] parameterTypes2 = {};
            Method method = Class.forName("LoveReflect$SubClass").getDeclaredMethod("subMethod", parameterTypes2);
            
            //用实例调方法
            method.invoke(subClass3, null);
            
            //通过反射处理数组
            SubClass[] subClass_ = {new SubClass(1,"bbbbbbbbbbbbbbb"), subClass, subClass2, subClass3};
            Class<?> arrayType = subClass_.getClass().getComponentType();
            System.out.println("array type="+arrayType.getName());
            System.out.println("array leangth="+Array.getLength(subClass_));
            System.out.println("first one="+((SubClass)Array.get(subClass_, 0)).getName());
            Array.set(subClass_, 0, subClass2);
            System.out.println("first one="+((SubClass)Array.get(subClass_, 0)).getName());
            
            //修改数组的大小
            SubClass[] newTemp=(SubClass[])arrayInc(subClass_,15);
            System.out.println("array leangth="+Array.getLength(newTemp));
            print(newTemp);
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InstantiationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SecurityException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (NoSuchFieldException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
    
    
       /**
     * 修改数组大小
     * */
    public static Object arrayInc(Object obj,int len){
        Class<?>arr=obj.getClass().getComponentType();
        Object newArr=Array.newInstance(arr, len);
        int co=Array.getLength(obj);
        System.arraycopy(obj, 0, newArr, 0, co);
        return newArr;
    }
    /**
     * 打印
     * */
    public static void print(Object obj){
        Class<?>c=obj.getClass();
        if(!c.isArray()){
            return;
        }
        System.out.println("数组长度为： "+Array.getLength(obj));
        for (int i = 0; i < Array.getLength(obj); i++) {
            System.out.print(Array.get(obj, i)+" ");
        }
    }
}