java if语句错误

发布于 2024-11-25 23:58:49 字数 290 浏览 1 评论 0原文

在我看来，这个 if 语句不起作用。

我是java新手，但我很了解C#和C++，但我以前从未见过这样的事情：

today=edit[0].substring(0,10);
if (today == edit[0].substring(0,10))
{
    pars_prog.addView(name_prog[i]);
}

而且它没有进入IF函数？

Java (Android) 中的 if 语句有何不同？

原文

It seems to me that this if statement is not working.

I'm new in java, but i know C# and C++ pretty well, but I've never seen such a thing before:

today=edit[0].substring(0,10);
if (today == edit[0].substring(0,10))
{
    pars_prog.addView(name_prog[i]);
}

And it doesn't get into the IF function?

Are if statements different in Java (Android)?

分享到QQ

分享到微博

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

需要登录才能够评论，你可以免费注册一个本站的账号。

芯好空 2024-12-02 23:58:49

当您对任何对象引用（无论是字符串还是任何其他非原始类型）使用 == 时，它只是比较引用是否相等 - 即它们是否引用了确切的对象相同的对象，或者它们是否都为空。

在本例中，您想要确定字符串是否相等 - 即它们是否表示相同的字符序列。为此，您应该使用 equals 方法：

if (today.equals(edit[0].substring(0,10)))

但是，通常在执行此操作时，您应该小心 equals 调用的目标为非空，否则您将得到一个NullPointerException。

请注意，C# 是相似 - 除了== 运算符可以重载，并且对于字符串 是重载的。如果操作数的编译时类型不都是string，您仍然会得到引用比较：

object text1 = new StringBuilder("hello").ToString();
object text2 = new StringBuilder("hello").ToString();
Console.WriteLine(text1 == text2); // False

When you use == for any object references (whether strings or any other non-primitive type) it simply compares whether the references are equal - i.e. whether they refer to the exact same object, or whether they're both null.

In this case, you want to determine whether the strings are equal - i.e. whether they represent the same sequence of characters. You should use the equals method for that:

if (today.equals(edit[0].substring(0,10)))

However, in general when doing this you should be careful that the target of the equals call is non-null, or you'll get a NullPointerException.

Note that C# is similar - except that the == operator can be overloaded, and is overloaded for string. If the compile-time types of the operands aren't both string, you'll still get reference comparison:

object text1 = new StringBuilder("hello").ToString();
object text2 = new StringBuilder("hello").ToString();
Console.WriteLine(text1 == text2); // False

回复收藏 0 原文