[Java基础]反射获取构造方法并使用练习

Posted 2021-08-15 Wecccccccc

Student类代码如下:

package ClassObjectPack;

public class Student {
    private String name;
    int age;
    public String address;

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

    public Student() {
    }

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

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

    private void function()
    {
        System.out.println("function");
    }

    public void method1()
    {
        System.out.println("method");
    }

    public void method2(String s)
    {
        System.out.println("method:"+s);
    }

    public String method3(String s,int i)
    {
        return s+","+i;
    }

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

代码如下:

package ClassObjectPack01;

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

public class ReflectDemo01 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
        Class<?> c = Class.forName("ClassObjectPack.Student");

        // public Student(String name, int age, String address)

        //Constructor<T> getConstructor(类<?>... parameterTypes)
        //返回一个 Constructor对象，该对象反映 Constructor对象表示的类的指定的公共 类函数。

        Constructor<?> con = c.getConstructor(String.class, int.class, String.class);

        // T newInstance(Object... initargs)
        // 使用此 Constructor对象表示的构造函数，使用指定的初始化参数来创建和初始化构造函数的声明类的新实例。

        Object obj = con.newInstance("林青霞", 30, "西安");
        System.out.println(obj);
    }
}

测试结果:

代码如下:

package ClassObjectPack01;

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

public class ReflectDemo02 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
        Class<?> c = Class.forName("ClassObjectPack.Student");


       //  private Student(String name)
        //Constructor<T> getConstructor(类<?>... parameterTypes)
        //返回一个 Constructor对象，该对象反映 Constructor对象表示的类的指定的公共 类函数。

        Constructor<?> con = c.getDeclaredConstructor(String.class);

        //我们无法通过私有构造创建对象
//        Object obj = con.newInstance("林青霞");
//        System.out.println(obj);

        //暴力反射
        //public void setAccessible (boolean flag):值为true,取消访问检查

        con.setAccessible(true);

        Object obj = con.newInstance("林青霞");
       System.out.println(obj);

    }
}

测试结果: