如何在 Java 中创建一些变量类型别名

假设我有这个密码

Map<String, String> list = new HashMap<String, String>();
list.put("number1", "one");
list.put("number2", "two");

我怎样才能使一些“别名”的类型

Map<String, String>

变得更容易被改写

// may be something like this
theNewType = HashMap<String, String>;


theNewType list = new theNewType();
list.put("number1", "one");
list.put("number2", "two");

基本上我的问题是，如何创建“别名”的一些“类型”，所以我可以使它更容易编写和更容易时，需要改变整个程序代码。

谢谢，如果这是个愚蠢的问题，抱歉，我对 Java 还是个新手。

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小开

Nothing like that exists in Java. You might be able to do something with IDE templates or autocompletion, and look forward to (limited) generics type inference in Java 7.

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最佳答案

There are no aliases in Java. You can extend the HashMap class with your class like this:

public class TheNewType extends HashMap<String, String> {
// default constructor
public TheNewType() {
super();
}
// you need to implement the other constructors if you need
}

But keep in mind that this will be a class it won't be the same as you type HashMap<String, String>

小开

There is no typedef equivalent in Java, and there is no common idiom for aliasing types. I suppose you could do something like

class StringMap extends HashMap<String, String> {}

but this is not common and would not be obvious to a program maintainer.

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The closest one could think of is to make a wrapper class like so

class NewType extends HashMap<String, String> {
public NewType() { }
}

I really wish Java had a sound type aliasing feature.

小开

Although Java doesn't support this, you can use a generics trick to simulate it.

class Test<I extends Integer> {
<L extends Long> void x(I i, L l) {
System.out.println(
i.intValue() + ", " +
l.longValue()
);
}
}

Source: http://blog.jooq.org/2014/11/03/10-things-you-didnt-know-about-java/