Java多线程设计模式详解学习笔记四——Immutable

public class Main { public static void main(String[] args) { Person alice = new Person("Alice", "Alaska"); new PrintPeronThread(alice).start(); new PrintPeronThread(alice).start(); new PrintPeronThread(alice).start(); } }public final class Person { private final String name; private final String address; public Person(String name,String address) { this.name=name; this.address=address; } @Override public String toString() { return "[Person: name: "+name+" ,address:"+address+"]"; } }public class PrintPeronThread extends Thread{ private Person person; public PrintPeronThread(Person person) { this.person=person; } @Override public void run() { while(true){ System.out.println(Thread.currentThread().getName()+" prints "+person); } } }

运行结果：

Thread-0 prints [Person: name: Alice ,address:Alaska] Thread-0 prints [Person: name: Alice ,address:Alaska] Thread-0 prints [Person: name: Alice ,address:Alaska] Thread-0 prints [Person: name: Alice ,address:Alaska] Thread-0 prints [Person: name: Alice ,address:Alaska] Thread-0 prints [Person: name: Alice ,address:Alaska] Thread-0 prints [Person: name: Alice ,address:Alaska] Thread-0 prints [Person: name: Alice ,address:Alaska] Thread-0 prints [Person: name: Alice ,address:Alaska] Thread-0 prints [Person: name: Alice ,address:Alaska] Thread-0 prints [Person: name: Alice ,address:Alaska] Thread-0 prints [Person: name: Alice ,address:Alaska]

何时使用：

1.当实例产生后，状态不再变化时

Immutable参与者是一个字段值无法改变的类，也没有任何用来改变字段的方法，所有字段设置成finall，Person没有setter方法。当Immutable参与者的实例创建以后，状态就完全不再变化。

2.实例需要共享，而且访问很频繁时

Immutable Pattern的优点，在于“不需要用synchronized保护”，这样的优点是在不丧失安全性与生命性的前提下，提高程序的执行性能。

final字段：

1.实例字段：

直接在声明字段的时候就直接赋初值

class Something{ final int value=123; }

在构造器中将值赋给字段（blank final）

class Something{ final int value; Something(){ this.value=123; } }2.静态变量

直接在声明字段的时候就直接赋初值

class Something{ final static int value=123; }

在static块（静态初始化）中将值赋给字段（blank fina）

class Something{ static final int value; static{ value=123; } }