Java中有没有一种方法可以基于java.lang基本类型（例如String）构建自定义类型？

Question

is there a way in Java to create a custom class based on a primitive Java base class to give the derived class a semantic?

Example: I want to create a LinkedHashMap<LastName, Age> ages where LastName is a custom type of String and Age a custom type derived from Integer . I just tried to create my own class

public class LastName extends String {
    //(no code in here, LastName has the same functionality as String)
}

but this is not possible. Is there another way to achieve what I want?

Answer 1

What you probably want is type-aliases. Java does not support this.

The best way would be to create a wrapper class, something like this:

class LastName{
    private String value;
} 

Another way is to name your variables correctly, eg don't do:

String string = "Smith";

But rather do:

String lastName = "Smith";

or just document your code with comments and javadoc.

---

Sidenote: If you still want to use type aliases you may want to use the Kotlin programming language which can compile to java-code (and more).

Answer 2

NO

Those classes are final.

Usual way to deal with it is to create wrapper class.

For example:

public class LastName {
    private final String value;
    public LastName(String value) {
        this.value = value;
    }
    public String get() { return value; } 
}

Answer 3

A String implements a CharSequence interface, just like StringBuffer and StringBuilder class. You can follow the same process.

public final class LastName implements CharSequence {

...

}