Java中反射reflect的基础知识讲解

    public static boolean isPrivate(int mod) {
        return (mod & PRIVATE) != 0;
    }

private final char value[];

import java.lang.reflect.Field;

public class ChangeStringValue {
	public static void main(String[] args) {
		String str = "hello";
		Class<?> clazz = String.class;
		try {
			Field field = clazz.getDeclaredField("value");
			field.setAccessible(true);
			//获取str对象中的value数组
			char[] value = (char[])field.get(str);
			value[0] = 'w';
			value[1] = 'o';
			value[2] = 'r';
			value[3] = 'l';
			value[4] = 'd';
		} catch (Exception e) {
			e.printStackTrace();
		}
		System.out.println(str);//world
	}
}

class User{
	protected int id;//id号
	public String name; //用户名
	private String password;//密码
    boolean checkName(String name){//实现代码}
    public User getName(String name){//实现代码}
    public void doSomething(){//实现代码}
    public void doSomething(String name,String password){//实现代码}
    public void doSomething(int id,String name,String password){//实现代码}
  }

class User {
	protected int id;// id号
	public String name; // 用户名
	private String password;// 密码

	boolean checkName(String name) {// 实现代码
		if("tom".equals(name) || "admin".equals(name))
			return true;
		else
			return false;
	}

	public String getName() {// 实现代码
		return name;
	}
	public String toString() {
		return "id="+id+",name="+name+",password="+password;
	}

	public void doSomething() {// 实现代码
		System.out.println("hello world");
	}

	public void doSomething(String name, String password) {// 实现代码
		System.out.println("name="+name+",password="+password);
	}

	public void doSomething(int id, String name, String password) {// 实现代码
		System.out.println("id="+id+",name="+name+",password="+password);
	}
}

public class Test1 {
	public static void main(String[] args) {
		String className = "com.briup.day17.que01.User";
		int id = 0;
		User u = null;
		try {
			Class c = Class.forName(className);
			u = (User)c.newInstance();
			Field[] fields = c.getDeclaredFields();
			for(Field f:fields) {
				int mod = f.getModifiers();
				String modifiers = Modifier.toString(mod);
				System.out.println(modifiers);
				if(Modifier.isPrivate(mod)) {
					//如果是私有属性，把它的访问权限设置为true
					f.setAccessible(true);
				}
				String fieldName = f.getName();
				System.out.println(fieldName);
				//给属性赋值
				Class<?> fieldType = f.getType();
				if(fieldType == int.class) {
					//说明它是id
					f.set(u, ++id);
				}else if(fieldType == String.class){
					if("name".equals(fieldName)) {
						f.set(u, "tom"+id);
					}else if("password".equals(fieldName)) {
						f.set(u, "123"+id);
					}
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
		System.out.println("==赋值以后的User对象==");
		System.out.println(u);
	}
}

public class Test2 {
	public static void main(String[] args) {
		//只调用了它的无参方法
		String className = "com.briup.day17.que01.User";
		User u = null;
		try {
			Class<?> c = Class.forName(className);
			u = (User)c.newInstance();
			Method[] methods = c.getDeclaredMethods();
			for(Method m:methods) {
				int mod = m.getModifiers();
				String modifiers = Modifier.toString(mod);
				System.out.println(modifiers);
				if(Modifier.isPrivate(mod)) {
					m.setAccessible(true);
				}
				Class<?> mreturnType = m.getReturnType();
				System.out.println(mreturnType.getSimpleName());
				String mName = m.getName();
				System.out.println(mName);
				Parameter[] parameters = m.getParameters();
				System.out.println(Arrays.toString(parameters));
				Object obj = null;
				if(parameters.length == 0) {
					//说明它是无参的
					if(Modifier.isStatic(mod)) {
						//静态的
						obj = m.invoke(null);
					}else {
						obj = m.invoke(u);
					}
					System.out.println("无参方法"+mName+"执行后的结果"+obj);
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

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

public class TestMain {
	public static void main(String[] args) throws Exception {
		String initName = "tom";
		Integer initAge = 18;
		String reName = "小张";
		Integer reAge = 12;
		String className = "com.briup.day17.que02.Person";
		Class<?> c = Class.forName(className);
		Class<?>[] parameterTypes = {String.class,Integer.class};
		Constructor<?> constructor = c.getConstructor(parameterTypes);
		Object[] initargs = {initName,initAge};
		Person p = (Person)constructor.newInstance(initargs);
		System.out.println("初始化后"+p);
		//使用反射的方式调用setName方法对名称进行赋值
		Method m = c.getDeclaredMethod("setName", String.class);
		m.invoke(p, reName);
		Field f = c.getDeclaredField("age");
		f.setAccessible(true);
		f.set(p, reAge);
		System.out.println("改值以后"+p);
	}
}

ObjectPool pool= new ObjectPool();
pool.initPool();
System.out.println(pool.getObject("student"));
System.out.println(pool.getObject("teacher"));

import java.io.FileWriter;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;

public class ObjectPool {
	private static Map<String, Object> objPool = new HashMap<>();

	public void initPool() {
		Properties prop = new Properties();
		prop.setProperty("student", "com.briup.day17.que03.Student");
		prop.setProperty("teacher", "com.briup.day17.que03.Teacher");
		FileWriter fw;
		try {
			fw = new FileWriter("./src/com/briup/day17/que03/msg.properties");
			prop.store(fw, "this is some Class msg");
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {
				if(fw != null)
					fw.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		Enumeration<?> enumeration = prop.propertyNames();
		while (enumeration.hasMoreElements()) {
			String key = (String) enumeration.nextElement();
			String value = prop.getProperty(key);
			objPool.put(key, createObj(value));
		}
	}

	// 创建一个方法 可根据String name 通过反射创建对象。
	public Object createObj(String className) {
		Class<?> c;
		Object obj = null;
		try {
			c = Class.forName(className);
			Constructor<?> constructor = c.getDeclaredConstructor();
			obj = constructor.newInstance();
		} catch (Exception e) {
			e.printStackTrace();
		}
		return obj;
	}

	// 创建一个方法 可根据名字从池子中取出对象。
	public Object getObject(String name) {
		return objPool.get(name);
	}
}

public class TestMain {
	public static void main(String[] args) {
		ObjectPool pool= new ObjectPool();
		pool.initPool();
		System.out.println(pool.getObject("student"));
		System.out.println(pool.getObject("teacher"));
	}
}