How to use upper bound wildcard in java

Explanation

1. The upper limit wildcard can be used to relax restrictions on variables.

For example, suppose you want to write a method that handles List, List and List, then you can achieve this by using upper bound wildcards.

2. The class instantiated by the upper bound wildcard must be the current class or a subclass of the current class.

3. If you want to declare an upper bound wildcard, please use a wildcard value.

Then comes the extends keyword, and finally its upper bound. Please note that in this context, extends is generally used to mean either extends (such as a class) or implements (such as an interface).

Example

public static void process(List<? extends Foo> list) {
    for (Foo elem : list) {
        // ...
    }
}

What can Java be used for?

Java is mainly used in:

1.web development;

2. Android development;

3. Client development;

4. Web development;

5. Enterprise application development;

6. Java big data development;

7. Game development, etc.

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