不可变对象(参考String类的实现)可采用的方式
1、将类声明为final(不能被继承)
2、将所有的成员声明为私有的(不能直接访问)
3、对变量不提供set方法,将所有可变的成员声明为final(只能赋值一次)
4、通过构造器初始化所有成员,进行深度拷贝
5、在get方法中不直接返回对象的本身,而是返回对象的拷贝
案例
package com.mmall.concurrency.example.immutable;
import com.google.common.collect.Maps;
import com.mmall.concurrency.annoations.ThreadSafe;
import lombok.extern.slf4j.Slf4j;
import java.util.Collections;
import java.util.Map;
public class ImmutableExample2 {
private static Map<Integer, Integer> map = Maps.newHashMap();
static {
map.put(1, 2);
map.put(3, 4);
map.put(5, 6);
map = Collections.unmodifiableMap(map);
}
public static void main(String[] args) {
map.put(1, 3);
log.info("{}", map.get(1));
}
}
package com.mmall.concurrency.example.immutable;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.mmall.concurrency.annoations.ThreadSafe;
public class ImmutableExample3 {
private final static ImmutableList<Integer> list = ImmutableList.of(1, 2, 3);
private final static ImmutableSet set = ImmutableSet.copyOf(list);
private final static ImmutableMap<Integer, Integer> map = ImmutableMap.of(1, 2, 3, 4);
private final static ImmutableMap<Integer, Integer> map2 = ImmutableMap.<Integer, Integer>builder()
.put(1, 2).put(3, 4).put(5, 6).build();
public static void main(String[] args) {
System.out.println(map2.get(3));
}
}
输出