在Java中使用接口内的固定类型约束？

Question

interface I1 { ... }
interface I2 { ... }
interface I3 { ... }
interface I4 { ... }

interface MyFactory {
  Object<? extends I1 & I2 & I3> createI1I2I3(); // doesn't work
  Object<? extends I2 & I3 & I4> createI2I3I4(); // doesn't work
}

Is there a trick to do it? I was thinking about things like

interface I1I2I3 extends I1, I2, I3 { ... }

But I1I2I3 != <? extends I1 & I2 & I3> <? extends I1 & I2 & I3> . There's a reason I just can't use this approach - I1 , I2 and I3 are foreign code.

Update

For those who curious why might someone need such a weird thing:

interface Clickable {}
interface Moveable {}
interface ThatHasText {}

interface Factory {
  Object<? extends Clickable> createButton(); // just a button with no text on it
  Object<? extends Clickable & ThatHasText> createButtonWithText();
  Object<? extends Moveable & ThatHasText> createAnnoyingBanner();
}

Answer 1

Object doesn't accept type parameter You can use the following construct instead:

interface I1 {  }
interface I2 {  }
interface I3 {  }
interface I4 {  }

interface MyFactory {
    public <T extends I1 & I2 & I3> T createI1I2I3(); 
    public <T extends I2 & I3 & I4> T createI2I3I4(); 
}

Answer 2

Your return type should be parameterized, so you can do

interface MyFactory {

   <T extends I1 & I2 & I3> T createI1I2I3();

}