package code; class Apple2{ T size; public Apple2(){} public Apple2(T size){ this.size = size; } public void setSize(T size){ this.size = size; } public T getSize(){ return this.size; } } public class GenericTest3{ public static void main(String[] args) { Apple2 a = new Apple2<>(6); Integer as = a.getSize(); Apple2 b = a; //泛型擦粗，当把一个带泛型信息的变量赋值给一个不带泛型信息的变量时，泛型信息会被擦除，默认是声明该泛型形参时的上限类型 Number bs = b.getSize(); System.out.println(bs); // Integer bs2 = b.getSize(); //此时会报错，泛型信息被擦除，因此bs类型应为Number Apple2 c = b; //泛型转换，这里b实际上引用的还是Apple2类型，因此这里c也应该是Apple2类型 Integer cs = c.getSize(); System.out.println(cs); } }