【高并发】06 不可变对象

一、不可变对象需要满足的条件

1、对象创建以后其状态就不能修改

2、对象所有域都是final类型

3、对象是正确创建的(在对象创建期间,this 引用没有逸出)

二、final关键字、修饰类方法变量

1、修饰类: 不能被继承

2、修饰方法:

锁定方法不被继承类修改 效率

3、修饰变量: 基本数据类型变量、引用类型变量

package com.current.flame.immutable; import com.current.flame.annoations.NotThreadSafe; import com.google.common.collect.Maps; import lombok.extern.slf4j.Slf4j; import java.util.Map; /** * @author haoxiansheng */ @Slf4j @NotThreadSafe public class ImmutableExample { public static void main(String[] args) { //a = 2; //b ="3"; //map = Maps.newHashMap(); // 不允许指向新的引用 log.info("map=>{}", map); map.put(1,4); log.info("map=>{}", map); } private final static Integer a = 1; private final static String b = "a"; private final static Map<Integer, Integer> map = Maps.newHashMap(); // 线程不安全 static { map.put(1,2); map.put(2,3); map.put(3,4); } private void testFinal(final int b) { //a = 1; } }

4、Collection.unmodifibleXXX:Collection、List、Set、Map…

package com.current.flame.immutable; import com.current.flame.annoations.ThreadSafe; import com.google.common.collect.Maps; import lombok.extern.slf4j.Slf4j; import java.util.Collections; import java.util.Map; /** * @author haoxiansheng */ @Slf4j @ThreadSafe public class ImmutableExample2 { public static void main(String[] args) { log.info("map=>{}", map); map.put(1,4); log.info("map=>{}", map); } private static Map<Integer, Integer> map = Maps.newHashMap(); // 线程不安全 static { map.put(1,2); map.put(2,3); map.put(3,4); map = Collections.unmodifiableMap(map); } }

5、Guava:ImmutableXXX:Collection、List、Set、Map…

package com.current.flame.immutable; import com.google.common.collect.ImmutableList; import com.google.common.collect.ImmutableMap; import com.google.common.collect.ImmutableSet; import lombok.extern.slf4j.Slf4j; /** * @author haoxiansheng */ @Slf4j public class ImmutableExample3 { private final static ImmutableList list = ImmutableList.of(1,2,2,3,4); 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) .build(); public static void main(String[] args) { //list.add(4); //运行出错 //set.add(3); //运行出错 //map.put(5,6); //运行出错 //map2.put(7,8); //运行出错 } }