关于java:Java中的反射

Java 反射机制，是在程序的运行过程中，对于任何一个类，都可能晓得它的所有属性和办法。对于任意一个对象，都可能晓得调用他的任意属性和办法。这种动静获取信息以及动静调用对象办法的性能称为 Java 语言的反射机制。

如下代码示例：

• 父类 Animal

package com.study.reflection;

public class Animal {
    public String name;
    public int age;

    public Animal() {super();
    }

    public Animal(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public void eat() {}

    public String getInfo() {return "name:" + this.name + ", age:" + age;}
}

• 子类 Cat，继承 Animal

package com.study.reflection;

public class Cat extends Animal {
    public String color;
    private String owner;
    String sex;

    public Cat() {super();
    }

    public Cat(String name, int age, String color, String owner) {super(name, age);
        this.color = color;
        this.owner = owner;
    }

    public Cat(String owner) {this.owner = owner;}

    public String getColor() {return color;}

    public void setColor(String color) {this.color = color;}

    void mie() {}

    private void smile() {System.out.println(name + "在笑");
    }

    public void cry() {System.out.println(name + "在哭");
    }

    @Override
    public String toString() {return "姓名：" + this.name + ", 年龄：" + this.age + ", 色彩：" + color + ", 客人：" + owner;}
}

• 测试类 TestReflect

package com.study.reflection;

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

public class TestReflect {public static void main(String[] args) {
        Class cat = null;
        try {cat = Class.forName("com.study.reflection.Cat");
        } catch (ClassNotFoundException e) {e.printStackTrace();
        }

        // 获取对象的所有私有（public）属性，例如：public String color; 包含继承的父类中 public 润饰的属性
        Field[] fields = cat.getFields();
        for (Field f : fields) {
            // 输入后果：// public java.lang.String com.study.reflection.Cat.color
            // public java.lang.String com.study.reflection.Animal.name
            // public int com.study.reflection.Animal.age
            System.out.println(f);
        }

        System.out.println("==========================================================");

        // 获取对象所有属性（不论是 public 还是 private 或者没有修饰符的润饰的属性），但不包含继承的父类中的属性
        Field[] declaredFields = cat.getDeclaredFields();
        for (Field df : declaredFields) {
            // 输入后果：//public java.lang.String com.study.reflection.Cat.color
            //private java.lang.String com.study.reflection.Cat.owner
            //java.lang.String com.study.reflection.Cat.sex
            System.out.println(df);
        }

        System.out.println("==========================================================");

        // 获取对象的所有公共（public）办法; 包含继承的父类中的 public 润饰的办法以及 Object 类中 public 润饰的办法
        Method[] methods = cat.getMethods();
        for (Method m : methods) {
            // 输入后果：//public java.lang.String com.study.reflection.Cat.toString()
            //public void com.study.reflection.Cat.setColor(java.lang.String)
            //public java.lang.String com.study.reflection.Cat.getColor()
            //public void com.study.reflection.Cat.cry()
            //public void com.study.reflection.Animal.eat()
            //public java.lang.String com.study.reflection.Animal.getInfo()
            //public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException
            //public final void java.lang.Object.wait() throws java.lang.InterruptedException
            //public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException
            //public boolean java.lang.Object.equals(java.lang.Object)
            //public native int java.lang.Object.hashCode()
            //public final native java.lang.Class java.lang.Object.getClass()
            //public final native void java.lang.Object.notify()
            //public final native void java.lang.Object.notifyAll()
            System.out.println(m);
        }

        System.out.println("==========================================================");

        // 获取对象所有办法（不论是 public 还是 private 或者没有修饰符的润饰的办法），但不包含继承的父类中的办法
        Method[] declaredMethods = cat.getDeclaredMethods();
        for (Method dm : declaredMethods) {
            // 输入后果：//public java.lang.String com.study.reflection.Cat.toString()
            //public void com.study.reflection.Cat.setColor(java.lang.String)
            //public java.lang.String com.study.reflection.Cat.getColor()
            //void com.study.reflection.Cat.mie()
            //private void com.study.reflection.Cat.smile()
            //public void com.study.reflection.Cat.cry()
            System.out.println(dm);
        }

        System.out.println("==========================================================");

        // 获取对象的所有公共（public）构造方法，但不包含继承的父类中的构造方法
        Constructor[] constructors = cat.getConstructors();
        for (Constructor c : constructors) {
            // 输入后果：//public com.study.reflection.Cat(java.lang.String)
            //public com.study.reflection.Cat(java.lang.String,int,java.lang.String,java.lang.String)
            //public com.study.reflection.Cat()
            System.out.println(c);
        }

        System.out.println("==========================================================");

        // 获取对象的所有构造方法，Constructor[] declaredConstructors = cat.getDeclaredConstructors();
        for (Constructor dc : declaredConstructors) {
            // 输入后果：//public com.study.reflection.Cat(java.lang.String)
            //public com.study.reflection.Cat(java.lang.String,int,java.lang.String,java.lang.String)
            //public com.study.reflection.Cat()
            System.out.println(dc);
        }

        System.out.println("==========================================================");

        //Cat cat1 = (Cat) cat.newInstance();// 此办法在 Java9 之后显示已过期
        Constructor<Cat> constructor = null;
        try {
            // 获取全参数构造函数
            constructor = cat.getConstructor(String.class, int.class, String.class, String.class);
        } catch (NoSuchMethodException e) {e.printStackTrace();
        }
        Cat cat1 = null;
        try {
            // 应用构造函数赋值初始化
            cat1 = constructor.newInstance("花花", 2, "红色", "小明");
        } catch (InstantiationException e) {e.printStackTrace();
        } catch (IllegalAccessException e) {e.printStackTrace();
        } catch (InvocationTargetException e) {e.printStackTrace();
        }
        // 输入后果：// 姓名：花花, 年龄：2, 色彩：红色, 客人：小明
        System.out.println(cat1);

        System.out.println("==========================================================");

        // 获取指定办法，并执行，【获取的办法必须是 public 润饰的】Method cry = null;
        try {
            // 输入后果：// 花花在哭
            cry = cat.getMethod("cry");//cry() 办法} catch (NoSuchMethodException e) {e.printStackTrace();
        }

        Object object = null;
        try {object = cry.invoke(cat1);// 调用 cry() 办法} catch (IllegalAccessException e) {e.printStackTrace();
        } catch (InvocationTargetException e) {e.printStackTrace();
        }
    }
}