java.lang.String 和 String 之间的类型不匹配错误
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Type mismatch error between java.lang.String and String
提问by StumpedCoder
This is really an odd problem, I've never encountered something like it. The following is a helper class I have declared inside a larger class. It runs perfectly fine as is:
这真是一个奇怪的问题，我从来没有遇到过这样的事情。以下是我在更大的类中声明的帮助类。它运行得很好：
private static class Tree<String> {
private Node<String> root;
public Tree(String rootData) {
root = new Node<String>();
root.data = rootData;
root.children = new ArrayList<Node<String>>();
}
private static class Node<String> {
String data;
Node<String> parent;
ArrayList<Node<String>> children;
}
}
However, by messing around I discovered a confounding problem. By replacing this line:
然而，通过乱搞，我发现了一个令人困惑的问题。通过替换这一行：
root.data = rootData;
with:
和：
root.data = "some string literal";
I get this error:
我收到此错误：
Type mismatch: cannot convert from java.lang.String to String
I tested out some string literal assignments in other classes and it appears to work perfectly fine. I recently updated to Java 1.7.0_15 and recently downloaded and installed Eclipse 4.2. I suspect there might be some confusion in the build path or something. Using Ubuntu 12.04
我在其他类中测试了一些字符串文字赋值，它似乎工作得很好。我最近更新到 Java 1.7.0_15，最近下载并安装了 Eclipse 4.2。我怀疑在构建路径或其他方面可能存在一些混乱。使用 Ubuntu 12.04
Any help would be greatly appreciated! I've searched and searched and couldn't find anything close to this problem.
任何帮助将不胜感激！我已经搜索并搜索过，但找不到与此问题接近的任何内容。
回答by j__m
You're creating a new generic type parameter named "String", which is probably not what you want.
您正在创建一个名为“String”的新泛型类型参数，这可能不是您想要的。
Change
改变
private static class Tree<String> {
to
到
private static class Tree {
回答by Jsdodgers
It seems like you are trying to create a generic class using "String" as the name of your generic type. What generic types do is whenever you create an object from the class, it replaces whatever is in the <>with the new type.
您似乎正在尝试使用“String”作为泛型类型的名称来创建泛型类。泛型类型的作用是，无论何时从类创建对象，它都会用<>新类型替换 中的任何内容。
So in your class, if you created a Tree<Integer>, ever instance of "String" in your class would be replaced by "Integer". This is the way some classes such as ArrayList work to allow any type to be used.
因此，在您的班级中，如果您在班级中创建了Tree<Integer>“String”的任何实例，则将被“Integer”替换。这是某些类（例如 ArrayList）允许使用任何类型的工作方式。
Usually when using generic types, a single letter, such as "T", is used to avoid it being the same as a real class type.
通常在使用泛型类型时，使用单个字母，例如“T”，以避免它与真正的类类型相同。
So in your case, you are trying to set a "String" that is not actually a String as an actual string.
因此，在您的情况下，您试图将实际上不是字符串的“字符串”设置为实际字符串。
回答by Learning
I solved it by typing
我通过输入解决了它
import java.lang.String;
