java default method sqrt instance usage

There are many methods that we can implement in the interface, among which the default method has attracted everyone's attention. Every time you want to implement a class and don't know where to start, besides using abstract methods, the default method sqrt is also a good choice. Let's briefly introduce one of these methods, and then bring the specific default method sqrt. Before that, let's have a brief understanding of other methods.

1. Java 8 allows us to use the default keyword to add non-abstract method implementations to interface declarations. This feature is also called an extension method. Here's our first example:

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

2. In the interface Formula, besides the abstract method caculate, a default method sqrt is defined. The Formula implementation class 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 as an anonymous object. The code is very wordy: It took 6 lines of code to realize a simple calculation function: a*100 square root.

Instance extension:

public class Test{ 
  public static void main(String args[]){
    double x = 11.635;
    double y = 2.76;

    System.out.printf("e  The value of is  %.4f%n", Math.E);
    System.out.printf("sqrt(%.3f)  For  %.3f%n", x, Math.sqrt(x));
  }
}

Compile the above program, and the output result is:

The value of e is 2.7183
sqrt (11.635) was 3.411