publicclassCovariantTest{publicAgetObj(){returnnewA();}publicstaticvoidmain(String[]args){CovariantTestc=newSubCovariantTest();System.out.println(c.getObj().x);}}classSubCovariantTestextendsCovariantTest{publicBgetObj(){returnnewB();}}classA{intx=5;}classBextendsA{intx=6;}上面的代码在编译运行时打印出5。它使用覆盖方法