Java之三种显示对象创建方式

内容来自孙卫琴的《Java面向对象编程》,做了小的修改

Java中有四种显示地创建对象的方式

1. 使用new语句创建
2. 运用反射手段,调用Class或者Constructor类的newInstance()方法
3. 调用对象的clone()方法
4. 运用反序列化手段

以下例子使用前三种方式创建,Customer是我们的测试类,clone方法调用了Object类的clone方法

package com.perficient.basic;

public class Customer implements Cloneable{
	private String name;
	private int age;

	public Customer() {
		this("unknown", 0);
		System.out.println("Call the defalut constructor");
	}
	
	public Customer(String name, int age) {
		this.name = name;
		this.age = age;
		System.out.println("Call the second constructor");
	}
	
	public Object clone()throws CloneNotSupportedException{
		return super.clone();
	}
	
	public boolean equals(Object o){
		boolean result=false;
		if (this == o) result = true;
		if (!(o instanceof Customer)) result = false;
		
		final Customer other = (Customer)o;
		if (this.name.equals(other.name)&& (this.age == other.age)){
			result = true;
		} else {
			result = false;
		}
				
		return result;
	}
	
	public String toString(){
		return "Name=" + this.name + ",age=" + this.age;
	}
}

以下是用来测试的main方法:

public static void main(String[] args) throws Exception{
		// 运用反射创建对象
		Class<?> objClass = Class.forName("com.perficient.basic.Customer");
		Customer c1 =(Customer)objClass.newInstance();      // 会调用类的默认构造方法
		System.out.println("c1:" + c1.toString());
		System.out.println("+++++++++++++++++++++++");
		
		// 使用New语句
		Customer c2 = new Customer("James", 20);
		System.out.println("c2:" + c2.toString());
		System.out.println("+++++++++++++++++++++++");
		
		// 用clone方法创建
		Customer c3 = (Customer) c2.clone();
		System.out.println("c2==c3: " + (c2 == c3));
		System.out.println("c2.equals(c3): " + (c2.equals(c3)));
		System.out.println("c3:" + c3.toString());
		System.out.println("+++++++++++++++++++++++");
	}

输出结果:

Call the second constructor
Call the defalut constructor
c1:Name=unknown,age=0
+++++++++++++++++++++++
Call the second constructor
c2:Name=James,age=20
+++++++++++++++++++++++
c2==c3: false
c2.equals(c3): true
c3:Name=James,age=20

总结

1.使用new语句以及newInstance()方法创建对象时,都会执行测试类的构造方法.
2.使用clone方法的时候不会调用构造方法
3.使用clone方法会创建一个复制的对象,这个对象与原来的对象具有不同的内存地址.所以使用==判断的时候,返回false