JAVA反射机制学习笔记_JAVA_编程开发_程序员俱乐部

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;
	}
}

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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());
	}
}

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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);
		}
	}
}

?config.properties

className=java.util.ArrayList

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