Java 11 and 12 – New Features

Adding generics to enums

Let's rewrite the enum code from the preceding example, adding a variable type to the enum Size. The bounded type parameter (<T extends Measurement>) restricts the types that can be passed as arguments to the Size enum, to the Measurement class and its derived classes.

This section modifies the code from the preceding section. To understand the example code and its purpose, please read the preceding section (if you haven't already). 

The modified code is as follows:

enum Size <T extends Measurement> {      // enum with type parameter 
    SMALL(new Small()), 
    MEDIUM(new Medium()), 
    LARGE(new Large()); 
 
    private T mObj; 
 
    Size(T obj) { 
        mObj = obj; 
    } 
    T getMeasurement() { 
        return mObj; 
    } 
} class Measurement {} class Small extends Measurement ...