JAVA反射学习笔记

public class ReflectPoint {

    private int x;
    public int y;
    
    public String str1 = "ball";
    public String str2 = "basketball";
    public String str3 = "itcast";
    
    public ReflectPoint(int x, int y) {
        super();
        this.x = x;
        this.y = y;
    }
    
    public int getX() {
        return x;
    }
    public void setX(int x) {
        this.x = x;
    }
    public int getY() {
        return y;
    }
    public void setY(int y) {
        this.y = y;
    }
}

import java.io.FileInputStream;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.Properties;
/*
 * HashSet 先判断是否存在该对象，如果存在则不放，
 * ArrayList是有顺序的，可以任意改变序号，人一个都可以放进去
 */
public class ReflectTest2 {

    public static void main(String[] args) throws Exception{

        /*
         * 配置文件的路径应该是相对与工程的目录，跟class和源文件的位置没有关系
         * 一定要用完整的路径，地址是运算出来的
         */
        
        InputStream ips = new FileInputStream("config.properties");
        Properties props = new Properties();
        props.load(ips);
        ips.close();
        String str = props.getProperty("className");
        Collection conllections = (Collection)Class.forName(str).newInstance();
        
        //Collection conllections = new ArrayList();
        //Collection conllections = new HashSet();
        ReflectPoint pt1 =new ReflectPoint(3,3);
        ReflectPoint pt2 =new ReflectPoint(5,5);
        ReflectPoint pt3 =new ReflectPoint(3,3);
        conllections.add(pt1);
        conllections.add(pt2);
        conllections.add(pt3);
        conllections.add(pt1);
        System.out.println(conllections.size());
    }
}

import java.lang.reflect.Array;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.Arrays;

public class ReflectTest {

    public static void main(String[] args) throws Exception{

        String str1 = "abc";
        Class cls1 = str1.getClass();
        Class cls2 = String.class;
        Class cls3;
    
            cls3 = Class.forName("java.lang.String");
            //字节码都是指向同一份——内存中的那个，所以下面的全部相等
            System.out.println(cls1 == cls2);
            System.out.println(cls2 == cls3);
            
            //判断某个类是否是基本类型
            System.out.println(cls1.isPrimitive());
            System.out.println(int.class.isPrimitive());
            
            System.out.println(int.class == Integer.class);
            //TYPE属性反映的是基本类型的那份字节码
            System.out.println(int.class == Integer.TYPE );
            
            //数组也是一种类型
            System.out.println(int[].class.isPrimitive());
            //判断某个对象或者类是否是数组类型用isArray()方法
            System.out.println(int[].class.isArray());
 
//new String(new StringBuffer("dsaf"));
            //Class --> Constructor --> Object
            //获得方法时要用的类型
            Constructor construct1 = String.class.getConstructor(StringBuffer.class);
            String str2 = (String)construct1.newInstance(new StringBuffer("abc"));
            System.out.println(str2);
            
            ReflectPoint pt1 = new ReflectPoint(3,5);
            Field fieldY = pt1.getClass().getField("y");
            //fieldY不是对象上的变量，而是类上，要用它去取某个对象上对应的Z值
            System.out.println(fieldY.get(pt1));
            
            Field fieldX = pt1.getClass().getDeclaredField("x");//让某个对象
            fieldX.setAccessible(true);//
            System.out.println(fieldX.get(pt1));
            
            //更改对象里面的属性，将a改为b
            changeStringValue(pt1);
            System.out.println("pt1.str1:" + pt1.str1);
            System.out.println("pt1.str2:" + pt1.str2);
            System.out.println("pt1.str3:" + pt1.str3);
            
            //str.charAt(1)
            //包名如果是用java打头的是标准，如果是用com打头则是公司所用
            Method methodCharAt = String.class.getMethod("charAt", int.class);
            System.out.println(methodCharAt.invoke(str1, 2));
            System.out.println(methodCharAt.invoke(str1, new Object[]{2}));
            
            //TestArguments.main(new String[]{new String("123"),new String("abc"),new String("xyz")});
            String startingClassName = args[0];
            Method mainMethod = Class.forName(startingClassName).getMethod("main", String[].class);
            /*
             * 这里必须封装一层Object数组，在invoke方法中会拆开，然后出现对象new String[]{new String("123"),
             * new String("abc"),new String("xyz")}一个string[]数组对象
             * 如果没有封装，则在invoke方法中直接拆开则参数会是new String("123"),new String("abc"),new String("xyz")三个对象
             */
            mainMethod.invoke(null,new Object[]{new String[]{new String("123"),new String("abc"),new String("xyz")}});
            
            int [] a1 = new int[]{1,2,3};
            int [] a2 = new int[4];
            int[][] a3 = new int[2][3];
            String[] a4 = new String[]{"a","b","c"};
            System.out.println(a1.getClass() == a2.getClass());
            System.out.println(a1.getClass().getName());
            System.out.println(a1.getClass().getSuperclass().getName());
            System.out.println(a1.getClass() == a4.getClass());
            System.out.println(a3.getClass().getName());
            System.out.println(a4.getClass().getSuperclass().getName());
            System.out.println(a1.getClass() == a3.getClass());
            
            //将数组遍历的方法Arrays.asList(),该类在utils包中
            System.out.println(a1);
            System.out.println(a4);
            //asList()方法对int类型不转换
            System.out.println(Arrays.asList(a1));
            System.out.println(Arrays.asList(a4));
            
            printObject(a4);
            printObject("xyz");
    }
 
/*
     * 对象的属性一定要是公共的，否则无法操作该属性的值
     */
    public static void changeStringValue(Object obj) throws Exception{
        Field[] fields = obj.getClass().getFields();
        System.out.println(fields.length);
        for(Field field : fields){
            //字节码只有一份，所以用==比较
            if(field.getType() == String.class){
                String odlStr = (String)field.get(obj);
                String newValue = odlStr.replace('b', 'a');
                field.set(obj, newValue);
            }
        }
    }
    
    public static void printObject(Object obj){
        Class clazz = obj.getClass();
        if(clazz.isArray()){
            int len = Array.getLength(obj);
            for(int i = 0; i < len; i++){
                System.out.println(Array.get(obj, i));
            }
        }else{
            System.out.println(obj);
        }
    }
}

class TestArguments{
    public static void main(String[]args){
        for(String arg : args){
            System.out.println(arg);
        }
    }
}

 

配置文件的代码config.properties

className=java.util.ArrayList