java中多个类的泛型类型

Question

How can achieve to boud a generic Type of a class to multiple calsses? A example is subclasses of Number and Boolean.

Answer 1

If I understand your question correctly, one of the options is to create additional enum-like class with limited number of instances:

public final class ValueType<T> {
    public static final ValueType<Boolean> BOOLEAN = new ValueType<>(Boolean.class);
    public static final ValueType<Integer> INTEGER = new ValueType<>(Integer.class);

    private final Class<T> clazz;

    private ValueType(Class<T> clazz) {
        this.clazz = clazz;
    }

    public Class<T> getType() {
        return clazz;
    }
}

Now your class can be declared this way:

public class MyClass<T> {
    public MyClass(ValueType<T> type) {
        Class<T> clazz = type.getType();
    }
}

So you can instantiate it like

MyClass<Boolean> c = new MyClass<>(ValueType.BOOLEAN);

Or

MyClass<Integer> c = new MyClass<>(ValueType.INTEGER);

But you have no other options, because you have no other ValueType objects.