简单总结下什么是Java反射，怎么使用。

Java反射机制

反射就是指JVM运行期，获取指定类所有的属性和方法的一种机制。

理解Class类

所有类通过JVM编译后就会生成一个Class对象，生成的对象保存在.class文件中，该文件包含了定义类的相关信息。

Java反射使用

Java反射.png

定义一个类

public class ReflectObject {
    public String name;
    private String username;

    public ReflectObject() {
    }

    @Override
    public String toString() {
        return "ReflectObject{" +
                "name='" + name + '\'' +
                ", username='" + username + '\'' +
                '}';
    }

    public void addName(String name, int year) {
        System.out.println("name:" + name + ",year:" + year);
    }
}

获取Class对象三种方法

public class ReflectTest {
    public static void main(String[] args) {
//        反射三种创建
//        1.对象获取
        ReflectObject object = new ReflectObject();
        Class class1 = object.getClass();
        System.out.println("class1=" + class1.getName());
//        2.类名
        Class class2 = ReflectObject.class;
        System.out.println("class2=" + class2.getName());
//        3.具体包名路径
        Class class3 = null;
        try {
            class3 = Class.forName("com.mysiga.learn.proxy.ReflectObject");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        System.out.println("class3=" + class3.getName());
}
}

输出

class1=com.mysiga.learn.proxy.ReflectObject
class2=com.mysiga.learn.proxy.ReflectObject
class3=com.mysiga.learn.proxy.ReflectObject

获取所有方法，成员变量，构造方法

public class ReflectTest {
    public static void main(String[] args) {
//        反射三种创建
//        1.对象获取
        ReflectObject object = new ReflectObject();
        Class class1 = object.getClass();
        System.out.println("class1=" + class1.getName());
//        2.类名
        Class class2 = ReflectObject.class;
        System.out.println("class2=" + class2.getName());
//        3.具体包名路径
        Class class3 = null;
        try {
            class3 = Class.forName("com.mysiga.learn.proxy.ReflectObject");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        System.out.println("class3=" + class3.getName());

//        获取成员方法Method
        StringBuilder methodBuilder = new StringBuilder();
        Method[] methods = class3.getDeclaredMethods();
//        Method[] methods = class3.getMethods();
        for (int i = 0; i < methods.length; i++) {
            methodBuilder.append(methods[i]).append("\n");

        }
        System.out.println("所有方法：" + methodBuilder.toString());

//                获取成员变量Field
        Field[] fields = class3.getFields();
        StringBuilder fieldBuilder = new StringBuilder();
        for (int i = 0; i < fields.length; i++) {
            fieldBuilder.append(fields[i]).append(",");
        }
        System.out.println("所有成员变量：" + fieldBuilder.toString());
        Method method = null;
        try {
            method = class3.getMethod("addName", String.class, int.class);
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
        if (method != null) {
            try {
                try {
                    method.invoke(class3.newInstance(),"Java",12);
                } catch (InstantiationException e) {
                    e.printStackTrace();
                }
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (InvocationTargetException e) {
                e.printStackTrace();
            }
        }
//        获取构造函数Constructor
        StringBuilder constructorBuilder = new StringBuilder();
        Constructor<?>[] constructors = class3.getConstructors();
        for (int i = 0; i < constructors.length; i++) {
            constructorBuilder.append(constructors[i]).append(",");
        }
        System.out.println("所有构造方法：" + constructorBuilder.toString());
    }
}

输出

class1=com.mysiga.learn.proxy.ReflectObject
class2=com.mysiga.learn.proxy.ReflectObject
class3=com.mysiga.learn.proxy.ReflectObject
所有方法：public java.lang.String com.mysiga.learn.proxy.ReflectObject.toString()
public void com.mysiga.learn.proxy.ReflectObject.addName(java.lang.String,int)

所有成员变量：public java.lang.String com.mysiga.learn.proxy.ReflectObject.name,
name:Java,year:12
所有构造方法：public com.mysiga.learn.proxy.ReflectObject(),