java反射的应用构造方法成员变量

男娘i 2022-06-09 03:28 213阅读 0赞

原文:[http://blognojava.iteye.com/blog/799068][http_blognojava.iteye.com_blog_799068]

由于有了神奇的Class的,基本反射也就是利用这个资源搞一搞,但是功能却很吓人....很多不好理解,很突然的东西

package com.itcast.test;
    
    import java.lang.reflect.Constructor;
    import java.lang.reflect.Field;
    
    public class Demo02 {
    	public static void main(String[] args) throws Exception{
    		//理解反射的概念,利用Class得到类的成分,对应的是Field Method Constuctor Package 等
    		
    		
    		//得到一个类的所有构造方法
    		
    		Constructor[] constructors=Class.forName("java.lang.String").getConstructors();
    		
    		//得到一个类的指定构造方法
    		Constructor construtor=Class.forName("java.lang.String").getConstructor(StringBuffer.class);
    		/*运行时异常-->>Exception in thread "main" java.lang.IllegalArgumentException: argument type mismatch
    		construtor.newInstance("abc");
    		*/
    		String str1=(String)construtor.newInstance(new StringBuffer("itcast"));
    		System.out.println(str1.charAt(2));
    		//在Class里面搞了一个便利的方法,直接给你构造方法,但无参的
    		
    		String str2=new String();
    		String str3=(String)Class.forName("java.lang.String").newInstance();
    		String str4=(String)str2.getClass().newInstance();
    		System.out.println(str2==null);
    		System.out.println(str2==str3);
    		System.out.println(str2==str4);
    		System.out.println(str3==str4);
    		
    		
    		//成员变量反射demo
    		ReflectPoint rP1=new ReflectPoint(3,5);
    		Field field1=rP1.getClass().getField("y");
    		//field值是多少?结果是:public int com.itcast.test.ReflectPoint.y
    		System.out.println(field1);
    		//用对象上的名字去取值 结果:5
    		System.out.println(field1.get(rP1));
    		
    		//同理取x
    		//Field field2=rP1.getClass().getField("x");
    		//报异常Exception in thread "main" java.lang.NoSuchFieldException: x
    		//System.out.println(field2);
    		//用另外的方式取值
    		Field field3=rP1.getClass().getDeclaredField("x");
    		System.out.println(field3);
    		/*取不到Exception in thread "main" java.lang.IllegalAccessException: 
    		Class com.itcast.test.Demo02 can not access a member o
    		System.out.println(field3.get(rP1));*/
    		//居然提供暴力方法
    		field3.setAccessible(true);
    		System.out.println(field3.get(rP1));
    
    	}
    
    }
    
    package com.itcast.test;
    
    public class ReflectPoint {
    	private int x;
    	public int y;
    
    	public ReflectPoint(int x, int y) {
    		this.x = x;
    		this.y = y;
    	}
    	
    
    }

一个反射小练习:把所有FieldValue中属性带有i的字母改成Y

package com.itcast.test;
    
    public class FieldString {
    	
    	public  String name="zhoujielun";
    	public  String address="taiwan";
    	public  String job="singer";
    	public int age=20;
    	@Override
    	public String toString() {
    		// TODO Auto-generated method stub
    		return "name:"+name+"address:"+address+"job:"+job+"age:"+age;
    	
    	}
    	
    	
    
    }
    package com.itcast.test;
    
    import java.lang.reflect.Field;
    
    public class test01 {
    	
    	public static void main(String[] args) throws Exception{
    		FieldString value1=new FieldString();
    		Field[] fields=value1.getClass().getFields();
    		for(Field field:fields){
    			//使用field.get()方式跟String类型做比较有问题,它返回时Object
    			
    			if(field.getType()==String.class){
    				String oldValue=(String)field.get(value1);
    				System.out.println(oldValue);
    				String newValue=oldValue.replace('i', 'Y');
    				field.set(value1, newValue);
    			}
    		}
    		System.out.println(value1);
    	}
    
    }

[http_blognojava.iteye.com_blog_799068]: http://blognojava.iteye.com/blog/799068