java创建对象的方式

总结

1、new

2、反射机制

3、clone机制，根据一个已有对象，克隆一个新对象。

4、序列化机制，先将一个对象序列化为二进制，再反序列化为java对象。

代码演示

下面的代码将会演示这四种创建对象的方式

我们要创建的的对象是一个Person类

java 复制代码

import java.io.Serializable;

public class Person implements Serializable, Cloneable {
    private static final long serialVersionUID = 1L;

    private String name;
    private int age;

    public Person() {
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

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

下面是main方法

java 复制代码

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class Main {
    public static void main(String[] args) throws Exception {
        // 1) new
        Person p1 = new Person("Alice", 20);
        print("new", p1);

        // 2) reflection
        Person p2 = Person.class.getDeclaredConstructor().newInstance();
        p2.setName("Bob");
        p2.setAge(21);
        print("reflection", p2);

        // 3) clone
        Person p3 = (Person) p1.clone();
        p3.setName("Alice-Clone");
        print("clone", p3);

        // 4) serialization
        Person p4 = serializeAndDeserialize(p1);
        print("serialization", p4);
    }

    private static void print(String label, Person person) {
        System.out.println(label + ": " + person + ", identityHashCode=" + System.identityHashCode(person));
    }

    private static Person serializeAndDeserialize(Person original) throws Exception {
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        try (ObjectOutputStream out = new ObjectOutputStream(bos)) {
            out.writeObject(original);
        }

        byte[] data = bos.toByteArray();
        try (ObjectInputStream in = new ObjectInputStream(new ByteArrayInputStream(data))) {
            return (Person) in.readObject();
        }
    }

}

输出

out 复制代码

new: Person{name='Alice', age=20}, identityHashCode=764977973
reflection: Person{name='Bob', age=21}, identityHashCode=189568618
clone: Person{name='Alice-Clone', age=20}, identityHashCode=793589513
serialization: Person{name='Alice', age=20}, identityHashCode=1190654826

面试

有四种方式，直接new对象，用反射机制动态创建对象，用clone机制复制一个新对象，用序列化机制的反序列化操作创建对象。