java上乘武功入门--反射

public class Test {
    private static void changeStrValue(String str, char[] value) {
    	// 只要执行魔法代码就可以达到下面的效果
        // 施展魔法的代码稍后揭秘
    }
    public static void main(String[] args) {
        changeStrValue("abc", new char[]{'d','e','f'});
        String abc = "abc";
        System.out.println("abc");
        System.out.println(abc);
        System.out.println("abc".equals(abc));
    }
}

import java.util.List;
public class Test {
    /**
     * 根据类名取得类实例
     * @author 二当家的白帽子 https://le-yi.blog.csdn.net/
     * @param className
     * @param <T>
     * @return
     * @throws InstantiationException
     * @throws IllegalAccessException
     * @throws ClassNotFoundException
     */
    public static <T> T getInstance(String className) throws InstantiationException, IllegalAccessException, ClassNotFoundException {
        Class<T> clazz = (Class<T>) Class.forName(className);
        return clazz.newInstance();
    }
    public static void main(String[] args) throws InstantiationException, IllegalAccessException, ClassNotFoundException {
        List<String> list = getInstance("java.util.ArrayList");
        list.add("abc");
        list.add("def");
        for (String v : list) {
            System.out.println(v);
        }
    }
}

import java.util.ArrayList;
public class Test {
     /**
     * 打印对象的类名
     * @author 二当家的白帽子 https://le-yi.blog.csdn.net/
     * @param o
     */
    public static void printClass(Object o) {
        System.out.printf(o.getClass().getName());
    }
    public static void main(String[] args) {
        printClass(new ArrayList<>());
    }
}

import java.lang.reflect.Field;
import java.lang.reflect.Method;
public class Test {
    /**
     * 打印类的属性
     * @author 二当家的白帽子 https://le-yi.blog.csdn.net/
     * @param clazz
     */
    public static void printFields(Class clazz) {
        System.out.println(clazz.getName() + "包含如下属性：");
        for (Field f : clazz.getDeclaredFields()) {
            System.out.println(f);
        }
    }
    /**
     * 打印类的方法
     * @author 二当家的白帽子 https://le-yi.blog.csdn.net/
     * @param clazz
     */
    public static void printMethods(Class clazz) {
        System.out.println(clazz.getName() + "包含如下方法：");
        for (Method m : clazz.getDeclaredMethods()) {
            System.out.println(m);
        }
    }
    public static void main(String[] args) {
        printFields(MyClass.class);
        printMethods(MyClass.class);
    }
}
class MyClass {
    private String name;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public class Test {
    /**
     * 调用一个对象的方法
     * @author 二当家的白帽子 https://le-yi.blog.csdn.net/
     * @param o
     * @param methodName
     * @throws NoSuchMethodException
     * @throws InvocationTargetException
     * @throws IllegalAccessException
     */
    public static void callMethod(Object o, String methodName) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        Method m = o.getClass().getDeclaredMethod(methodName);
        m.setAccessible(true);
        m.invoke(o);
    }
    /**
     * 修改一个对象的属性
     * @author 二当家的白帽子 https://le-yi.blog.csdn.net/
     * @param o
     * @param fieldName
     * @param value
     * @throws IllegalAccessException
     */
    public static void changeFieldValue(Object o, String fieldName, Object value) throws NoSuchFieldException, IllegalAccessException {
        Field f = o.getClass().getDeclaredField(fieldName);
        f.setAccessible(true);
        f.set(o, value);
    }
    public static void main(String[] args) throws InvocationTargetException, NoSuchMethodException, IllegalAccessException, NoSuchFieldException {
        MyClass o = new MyClass();
        // 修改任意属性，即使是私有的
        changeFieldValue(o, "name", "二当家的白帽子");
        // 调用任意方法，即使是私有的
        callMethod(o, "printName");
    }
}
class MyClass {
	// 私有属性，只可以调用set方法修改
    private String name;
    private void printName() {
        // 私有方法，只有本类自己的实例可以调用
        System.out.println("My name is " + name);
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

import java.lang.reflect.Field;
public class Test {
    /**
     * 修改字符串内部的值
     * @author 二当家的白帽子 https://le-yi.blog.csdn.net/
     * @param str
     * @param value
     */
    private static void changeStrValue(String str, char[] value) {
        try {
            Field f = str.getClass().getDeclaredField("value");
            f.setAccessible(true);
            f.set(str, value);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    public static void main(String[] args) {
        changeStrValue("abc", new char[]{'d','e','f'});
        // 这里的"abc"字符串和上面调用changeStrValue的参数"abc"会指向同一块内存
        String abc = "abc";
        System.out.println("abc");
        System.out.println(abc);
        System.out.println("abc".equals(abc));
    }
}