Java反射的使用

一、常用方法

在熟悉方法前我们先建立两个类用于后面使用 Student和Person

• Student

public class Student extends Person{
    public String name;
    private int age;

    public Student() {
        name = "name";
        age = 0;
    }

    public Student(String name, int age) {
        setName(name);
        setAge(age);
    }
    private Student(String name) {
        setName(name);
        setAge(-1);
    }

    public String getName() {
        return name;
    }
    @Deprecated
    public int getAge() {
        return age;
    }

    private Student setName(String name) {
        this.name = name;
        return this;
    }

    private Student setAge(int age) {
        this.age = age;
        return this;
    }
    private void print(String name){
        System.out.println("print "+name);
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", id=" + id +
                '}';
    }
}

• Person

public class Person {
    int id;

    public int getId() {
        return id;
    }

    public Person setId(int id) {
        this.id = id;
        return this;
    }
    private void run(){
        System.out.println("person run");
    }
}

1. 获取class的方法

Student stu = new Student();
Class stuClass = stu.getClass();
stuClass = Student.class;
stuClass = Class.forName("com.jlhlyby.java.reflex.Student");
/**所有获取方式获取的class都是相同的对象，一个类只有一个class对象*/

2.获取构造方法

//获取所有公有构造函数
Constructor[] constructors = stuClass.getConstructors();
//获取所有构造函数（包含非公有）
Constructor[] declaredConstructors = stuClass.getDeclaredConstructors();

//获取无参公有构造函数
Constructor constructor = stuClass.getConstructor();
//获取构造函数（包含非公有）
Constructor decConstructor = stuClass.getDeclaredConstructor(String.class);
//获取有参数构造函数
Constructor paramConstructor =  stuClass.getConstructor(String.class,int.class);

3.构建实例

Student instance = (Student) constructor.newInstance();
Student instance1 = (Student) paramConstructor.newInstance("test",20);
//暴露访问（忽略访问权限）
decConstructor.setAccessible(true);
Student instance2 = (Student) decConstructor.newInstance("testDeclared");

4.获取字段

//所有公有字段
Field[] fields = stuClass.getFields();
//获取所有字段（包含非公有）
Field[] decFields = stuClass.getDeclaredFields();
//通过字段名获取公有字段
Field nameField = stuClass.getField("name");
//通过字段名获取字段(包含非公有）
Field ageField = stuClass.getDeclaredField("age");
ageField.setAccessible(true);
//获取某对象字段值
int age = (int) ageField.get(instance2);
//修改某对象字段值
ageField.set(instance2,2);
System.out.println("age: "+age+" -> "+  instance2.getAge());

5.获取方法

Method[] methods = stuClass.getMethods();
Method[] decMethods =  stuClass.getDeclaredMethods();
Method printMethod =  stuClass.getDeclaredMethod("print",String.class);
printMethod.setAccessible(true);
printMethod.invoke(stu,"test");

6.其他

//获取父类
stuClass.getSuperclass();
//获取接口
stuClass.getInterfaces();
//获取注解
stuClass.getAnnotations();
nameField.getAnnotations(); 

7.输出下上面的结果

 System.out.println("class: "+stuClass.getName());
        System.out.println();
        for (Constructor cons:constructors) {
            System.out.println("cons: "+cons);
        }
        System.out.println();
        for (Constructor cons:declaredConstructors) {
            System.out.println("declaredCons: "+cons);
        }
        System.out.println();
        System.out.println("constructor: "+constructor);
        System.out.println("decConstructor: "+constructor);
        System.out.println("paramConstructor param: "+paramConstructor.getParameterTypes());
        System.out.println("instance: "+instance);
        System.out.println("instance1: "+instance1);
        System.out.println("instance2: "+instance2);
        System.out.println();
        for (Field field : fields) {
            System.out.println("field: "+field);
        }
        System.out.println();
        for (Field decField : decFields) {
            System.out.println("field: "+decField);
        }
        System.out.println();
        System.out.println("nameField: "+nameField);
        System.out.println("ageField: "+ageField);
        System.out.println();
        for (Method m : methods){
            System.out.println("method: "+m);
        }
        for (Method m:decMethods){
            System.out.println("decMethods: "+m);
        }

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