How to use wildcards in java method parameters

Explanation

1. Wildcard? super Fruit limits the lower bound of the generic to Fruit.

2. Generic objects and Generic objects can be passed to print2 as parameters. However, the Generic object cannot be passed in as a parameter, because Apple is a subclass of Fruit and exceeds the lower bound of generics.

Example

Generic<Fruit> fruitGeneric2 = new Generic<>();
print2(fruitGeneric2);
 
Generic<Food> foodGeneric2 = new Generic<>();
print2(foodGeneric2);
 
//    错误使用
//    Generic<Apple> appleGeneric2 = new Generic<>();
//    print2(appleGeneric2);

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