JAVA反射-反射对构造方法的操作

构造方法在 反射中的类是 Constructor!

package com.northcastle.groupconstructor;


public class Dog {
    private String name;
    private Integer age;

    //准备一批构造方法
    public Dog() {
    }

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

    public Dog(Integer age) {
        this.age = age;
    }

    public Dog(String name, Integer age) {
        this.name = name;
        this.age = age;
    }
}

getConstructors() : 获取所有的 public 的构造方法
getDeclaredConstructors() ： 获取所有的构造方法

package com.northcastle.groupconstructor;

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


public class Application {
    public static void main(String[] args) throws ClassNotFoundException {
        //1.创建Class类的对象
        String classPath = "com.northcastle.groupconstructor.Dog";
        Class clazz = Class.forName(classPath);

        //2.获取所有的构造器的列表
        Constructor[] constructorList = clazz.getConstructors();
        Constructor[] declaredConstructorList = clazz.getDeclaredConstructors();
        for (Constructor constructor : constructorList) {
            System.out.println(constructor);
        }
        System.out.println("======================");
        for (Constructor constructor : declaredConstructorList) {
            System.out.println(constructor);
        }

    }
}

#运行结果
public com.northcastle.groupconstructor.Dog(java.lang.String,java.lang.Integer)
public com.northcastle.groupconstructor.Dog(java.lang.Integer)
public com.northcastle.groupconstructor.Dog()
======================
public com.northcastle.groupconstructor.Dog(java.lang.String,java.lang.Integer)
public com.northcastle.groupconstructor.Dog(java.lang.Integer)
private com.northcastle.groupconstructor.Dog(java.lang.String)
public com.northcastle.groupconstructor.Dog()

getConstructor(参数类型列表) ：获取指定的public 的构造方法；
getDeclaredConstructor(参数类型列表) ：获取指定的构造方法

package com.northcastle.groupconstructor;

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


public class Application {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException {
        //1.创建Class类的对象
        String classPath = "com.northcastle.groupconstructor.Dog";
        Class clazz = Class.forName(classPath);
        
        //3.获取指定的构造方法
        Constructor constructor = clazz.getConstructor(Integer.class);
        Constructor declaredConstructor = clazz.getDeclaredConstructor(String.class);
        System.out.println(constructor);
        System.out.println(declaredConstructor);

    }
}

# 运行结果
public com.northcastle.groupconstructor.Dog(java.lang.Integer)
private com.northcastle.groupconstructor.Dog(java.lang.String)

getModifiers() : 以int形式返回修饰符
【default = 0 ; public = 1; private = 2; protected = 4; static = 8;final = 16】

package com.northcastle.groupconstructor;

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


public class Application {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException {
        //1.创建Class类的对象
        String classPath = "com.northcastle.groupconstructor.Dog";
        Class clazz = Class.forName(classPath);

        //4.获取构造方法的修饰符
        Constructor declaredConstructor2 = clazz.getDeclaredConstructor(String.class);
        int modifiers = declaredConstructor2.getModifiers();
        System.out.println(declaredConstructor2); // private = 2
        System.out.println(modifiers);
    }
}

# 运行结果
private com.northcastle.groupconstructor.Dog(java.lang.String)
2

getName()

package com.northcastle.groupconstructor;

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


public class Application {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException {
        //1.创建Class类的对象
        String classPath = "com.northcastle.groupconstructor.Dog";
        Class clazz = Class.forName(classPath);

        //5.获取构造方法的全类名
        Constructor declaredConstructor3 = clazz.getDeclaredConstructor(String.class);
        String name = declaredConstructor3.getName();
        System.out.println(name);
    }
}

# 运行结果
com.northcastle.groupconstructor.Dog

getParameterTypes() : 以Class[] 类型返回构造方法的参数列表

package com.northcastle.groupconstructor;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.Arrays;


public class Application {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException {
        //1.创建Class类的对象
        String classPath = "com.northcastle.groupconstructor.Dog";
        Class clazz = Class.forName(classPath);

        //6.获取构造方法的参数列表
        Constructor[] list = clazz.getDeclaredConstructors();
        for (Constructor constructor1 : list) {
            Class[] parameterTypes = constructor1.getParameterTypes();
            System.out.println(constructor1);
            System.out.println(Arrays.toString(parameterTypes));
            System.out.println("***");
        }
    }
}

# 运行结果
public com.northcastle.groupconstructor.Dog(java.lang.String,java.lang.Integer)
[class java.lang.String, class java.lang.Integer]
***
public com.northcastle.groupconstructor.Dog(java.lang.Integer)
[class java.lang.Integer]
***
private com.northcastle.groupconstructor.Dog(java.lang.String)
[class java.lang.String]
***
public com.northcastle.groupconstructor.Dog()
[]
***

newInstance(构造方法的参数) :

package com.northcastle.groupconstructor;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
import java.util.Arrays;


public class Application {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
        //1.创建Class类的对象
        String classPath = "com.northcastle.groupconstructor.Dog";
        Class clazz = Class.forName(classPath);

        //7.使用构造方法创建对象
        Constructor declaredConstructor1 = clazz.getDeclaredConstructor(String.class, Integer.class);
        Object aa = declaredConstructor1.newInstance("aa", 3);
        Class aClass = aa.getClass(); // 创建的对象的运行时类型
        System.out.println(aClass);
        if (aa instanceof Dog){
            System.out.println("对象aa的确是Dog类型");
            Dog d = (Dog) aa;
            System.out.println(d);
        }else{
            System.out.println("对象aa不是Dog类型");
        }
    }
}

# 运行结果
class com.northcastle.groupconstructor.Dog
对象aa的确是Dog类型
Dog{name='aa', age=3}

Congratulations!
You are one step closer to success!