字符串是Java中的对象，那么为什么我们不使用“new”来创建它们呢？ [英] Strings are objects in Java, so why don't we use 'new' to create them?

问题描述

我们通常使用 new 关键字创建对象，例如：

We normally create objects using the new keyword, like:

Object obj = new Object();

字符串是对象，但我们不使用 new 创建它们：

Strings are objects, yet we do not use new to create them:

String str = "Hello World";

这是为什么？我可以用 new 制作一个字符串吗？

Why is this? Can I make a String with new?

推荐答案

除了什么已经说过，字符串文字 [即字符串如abcd但不像新字符串（abcd）在Java中实现] - 这意味着每次引用abcd时，都会获得对单个 String 实例的引用，而不是每次一个新的。所以你将拥有：

In addition to what was already said, String literals [ie, Strings like "abcd" but not like new String("abcd")] in Java are interned - this means that every time you refer to "abcd", you get a reference to a single String instance, rather than a new one each time. So you will have:

String a = "abcd";
String b = "abcd";

a == b; //True

但如果你有

String a = new String("abcd");
String b = new String("abcd");

然后可以

a == b; // False

（如果有人需要提醒，请始终使用 .equals （）比较字符串; == 测试物理相等性。）

(and in case anyone needs reminding, always use .equals() to compare Strings; == tests for physical equality).

实习字符串文字是好的，因为它们经常被使用多次。例如，考虑（设计的）代码：

Interning String literals is good because they are often used more than once. For example, consider the (contrived) code:

for (int i = 0; i < 10; i++) {
  System.out.println("Next iteration");
}

如果我们没有字符串实习，则需要下一次迭代要实例化10次，而现在它只会被实例化一次。

If we didn't have interning of Strings, "Next iteration" would need to be instantiated 10 times, whereas now it will only be instantiated once.

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