Immutable

想破坏也破坏不了。

Immutable 可以确保实例状态不发生改变，访问这类实例时不需要执行耗时的互斥处理，可以提升性能。

实际案例

定义

  • Person.java

不可变对象类

  [java]
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/**
 * 不可变类
 *
 * @author bbhou
 * @version 1.0.0
 * @since 1.0.0
 */
public final class Person {

    private final String name;

    private final String address;

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

    public String getName() {
        return name;
    }

    public String getAddress() {
        return address;
    }

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

}
  • PrintPersonThread.java

线程类

  [java]
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public class PrintPersonThread extends Thread {

    private Person person;

    public PrintPersonThread(Person person) {
        this.person = person;
    }

    @Override
    public void run() {
        int limit = 100;
        for(int i = 0; i< limit; i++) {
            System.out.println(Thread.currentThread().getName()+":  " + person);
        }
    }

}

测试

  • 运行
  [java]
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public class Main {

    public static void main(String[] args) {
        Person person = new Person("as", "asdf");
        new PrintPersonThread(person).start();
        new PrintPersonThread(person).start();
        new PrintPersonThread(person).start();
    }

}
  • 测试结果
  [plaintext]
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...
Thread-1:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-0:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-0:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-0:  Person{name='as', address='asdf'}
Thread-0:  Person{name='as', address='asdf'}
Thread-0:  Person{name='as', address='asdf'}
Thread-0:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-0:  Person{name='as', address='asdf'}
Thread-2:  Person{name='as', address='asdf'}
Thread-0:  Person{name='as', address='asdf'}
Thread-0:  Person{name='as', address='asdf'}
Thread-0:  Person{name='as', address='asdf'}
...

实现方式

  • 确保类不会被覆写 （1）一般是用 final 修饰不可变类 （2）或者使用静态工厂创建方法，确保构造函数私有的

  • 字段不可变 所有的字段必须是私有的，并且加上修饰符 final

  • 不提供改变对象的方法 此处不单单指 setter，所有修改状态的方法都要避免

  • 如果存在可变字段 则必须进行保守型复制，且只能由该类自身进行修改

适用场景

  • 实例创建后，状态不再发生变化

  • 实例是被共享的，且频繁被访问

UML & Code

  • UML

UML关系

  • 代码地址

immutable

系列导航

多线程系列导航