Java – enumeration with getter

Can enumerations use vendors to store references to getter methods?

Use this:

String value = myEnum.getValue(object)

I can't imagine how to write it without compiling errors

Solution

If all getters have the same return type, it is not very difficult Consider the following POJO classes:

public static class MyPoJo {
    final String foo,bar;

    public MyPoJo(String foo,String bar) {
        this.foo = foo;
        this.bar = bar;
    }

    public String getFoo() {
        return foo;
    }

    public String getBar() {
        return bar;
    }

    public int getBaz() {
        return 5;
    }
}

Then we may have such an enumeration:

public static enum Getters {
    FOO(MyPoJo::getFoo),BAR(MyPoJo::getBar);

    private final Function<MyPoJo,String> fn;

    private Getters(Function<MyPoJo,String> fn) {
        this.fn = fn;
    }

    public String getValue(MyPoJo object) {
        return fn.apply(object);
    }
}

And use it like this:

System.out.println(Getters.FOO.getValue(new MyPoJo("fooValue","barValue"))); // fooValue

However, if you want to return different types, there will be a problem In this case, I recommend using normal classes with predefined instances instead of enumerations:

public static final class Getters<T> {
    public static final Getters<String> FOO = new Getters<>(MyPoJo::getFoo);
    public static final Getters<String> BAR = new Getters<>(MyPoJo::getBar);
    public static final Getters<Integer> BAZ = new Getters<>(MyPoJo::getBaz);

    private final Function<MyPoJo,T> fn;

    private Getters(Function<MyPoJo,T> fn) {
        this.fn = fn;
    }

    public T getValue(MyPoJo object) {
        return fn.apply(object);
    }
}

The usage is the same:

System.out.println(Getters.FOO.getValue(new MyPoJo("fooValue","barValue"))); // fooValue
System.out.println(Getters.BAZ.getValue(new MyPoJo("fooValue","barValue"))); // 5