请参见以下代码段。
Integer xInteger = new Integer(1);
map.put('c', xInteger);
xInteger++;
System.out.println(xInteger); // 2
System.out.println(map.get('c')); // 1
System.out.println(xInteger == map.get('c')); // false
我知道HashMap使用Node数组存储K，V对象。但是在这里，哈希表似乎只存储Integer的原始值？因为从HashMap检索的值对象甚至不是我们之前放置的对象。有谁知道hashmap如何处理包装类？
Primitives, primitive wrapper objects, and a number of other types (e.g.
java.lang.String) are immutable. Their internal state cannot be changed.The only way to update the value of an
Integerin a map, is to assign a newIntegerto the map entry:As of Java 1.5, Java performs auto-unboxing to convert "wrapper types" such as Integer to the corresponding primitive type
intwhen necessary. Then the increment operator can work on the resultingint.When you do
xInteger++, it performs that on the primitiveint. Since primitiveintis immutable (so is it's wrapper), it is not reflected when you doSystem.out.println(map.get('c')).您可以直接写：