Java – why doesn’t class have a good generic type in this case?

In this code, why can't you declare a type as class? Extension b >

public class Foo<B> {
    public void doSomething(B argument) {
        Class<? extends Object> type = argument.getClass();
    }
}

Solution

The problem is that Java syntax does not allow getClass () to indicate that it returns a type that matches its defined class, and this is not a special case for the compiler So you were forced to surrender

In many cases, you want to be able to specify this type, for example, for links, so I want them to include this feature one day

You can write

Class<? extends this> getClass();

or

public this clone(); // must return a type of this class.

or

class ByteBuffer {
    this order(ByteOrder order);
}

class MappedByteBuffer extends ByteBuffer {
}

// currently this won't work as ByteBuffer defines order()
MappedByteBuffer mbb = fc.map(MapMode.READ_WRITE,fc.size())
                         .order(ByteOrder.nativeOrder());