How to use java default method sqrt

1. Java 8 allows us to use the default keyword to add non-abstract method implementations to interface declarations. This feature is also known as extension method. The following is our first example:

interface Formula {
    double calculate(int a);
 
    default double sqrt(int a) {
        return Math.sqrt(a);
    }
}

2. In the interface Formula, in addition to the abstract method caculate, a default method sqrt is also defined. The implementation class of Formula only needs to implement the abstract method caculate. The default method sqrt can be used directly.

Formula formula = new Formula() {
    @Override
    public double calculate(int a) {
        return sqrt(a * 100);
    }
};
 
formula.calculate(100);     // 100.0
formula.sqrt(16);           // 4.0

The formula object implements the Formula interface in the form of an anonymous object. The code is very verbose: it took 6 lines of code to implement a simple calculation function: the square root of a*100.

What collection classes are there in Java?

Collections in Java are mainly divided into four categories:

1. List: ordered, repeatable;

2. Queue: ordered and repeatable;

3. Set: non-repeatable;

4. Map: unordered, with unique keys and non-unique values.

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