new Integer(123)、Integer.valueOf(123) 和 just 123 之间的区别
最近我看到这样的代码(Java):
Recenlty I saw code (Java) like this:
myMethod(new Integer(123));
我目前正在重构一些代码，Sonar 工具中有一个提示，使用这样的东西对内存更友好:
I am currently refactoring some code, and there is a tip in Sonar tool, that it's more memory friendly to use sth like this:
myMethod(Integer.valueOf(123));
但是在这种情况下，我认为如果我会使用没有区别:
However in this case, I think that there is no difference if I would use:
myMethod(123);
我可以理解，如果我将变量传递给方法，但硬编码 int?或者如果会有 Long/Double 等，我想要 Long 表示数字.但是整数?
I could understand that, if I would pass a variable to the method, but hard coded int? Or if there would be Long/Double etc and I want Long representation of number. But integer?
推荐答案
new Integer(123) 将为每个调用创建一个新的 Object 实例.
new Integer(123) will create a new Object instance for each call.
根据 javadoc, Integer.valueOf(123) 不同之处在于它缓存对象......所以如果你调用它更多，你可能(或可能不会)最终得到相同的 Object不止一次.
According to the javadoc, Integer.valueOf(123) has the difference it caches Objects... so you may (or may not) end up with the same Object if you call it more than once.
比如下面的代码:
public static void main(String[] args) {
Integer a = new Integer(1);
Integer b = new Integer(1);
System.out.println("a==b? " + (a==b));
Integer c = Integer.valueOf(1);
Integer d = Integer.valueOf(1);
System.out.println("c==d? " + (c==d));
}
有以下输出:
a==b? false
c==d? true
至于使用 int 值，您使用的是原始类型(考虑到您的方法也在其签名上使用原始类型) - 它会使用更少的内存并且可能更快，但是您例如，不能将其添加到收藏中.
As to using the int value, you are using the primitive type (considering your method also uses the primitive type on its signature) - it will use slightly less memory and might be faster, but you won't be ale to add it to collections, for instance.
如果您的方法的签名，还请查看 Java 的 AutoBoxing使用 Integer - 使用时，JVM 会自动为您调用 Integer.valueOf()(因此也使用缓存).
Also take a look at Java's AutoBoxing if your method's signature uses Integer- when using it, the JVM will automatically call Integer.valueOf() for you (therefore using the cache aswell).
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