How to use lower bound wildcard in java

Explanation

1. The lower limit wildcard limits unknown types to specific types or supertypes.

2. The lower bound wildcard uses the wildcard character ('?').

means that it is followed by the super keyword, and then its lower limit .

3. The class instantiated under the wildcard must be the current class or the superclass of the current class.

When storing data, the data type can only be the current class or the superclass of the current class.

Examples

public static void addNumbers(List<? super Integer> list) {
    for (int i = 1; i <= 10; i++) {
        list.add(i);
    }
}

What collection classes are there in Java

Collections in Java are mainly divided into four categories:

1, List List: ordered, repeatable;

2, Queue queue: ordered, repeatable;

3, Set collection: non-repeatable;

4, Map mapping: unordered, unique keys, non-unique values.

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