Java Streams Examples

import java.util.Arrays;
import java.util.*;
import java.util.stream.*;
import java.time.*;

public class HelloWorld{

     public static void main(String []args){
        System.out.println("Hello World");
    
        Formula formula = new Formula() {
            @Override
            public double calculate(double a, double b) {
                return a*b;
            }
        };
        formula.calculate(10.9,93.0);
        formula.showValue(29.0); 

        showLambada();

       functionalInterfaceExample();
       
     }
}
//

Default Methods for Interfaces

interface Formula {
    double calculate(double a, double b);
   
    default void showValue(double sum){
        System.out.println("sum value is "+sum);
    }
}

public void showLambada(){

        //LAMBADA EXPRESSION.

        //Old way of sorting.
        List<String> names = Arrays.asList("peter", "anna", "mike", "xenia");

        Collections.sort(names, new Comparator<String>() {
            @Override
            public int compare(String a, String b) {
                return b.compareTo(a);
            }
        });
        //with lambada expression.
        Collections.sort(names, (String a, String b)-> b.compareTo(a));
       
        Collections.sort(names, (a,b)-> b.compareTo(a));
       
        //Collecting a list in upper case
        List aaList = names.stream().map(s->s.toUpperCase()).filter(s->s.length()>3)
                      .collect(Collectors.toList());
                     
        System.out.println(aaList);
}
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Functional Interfaces:

@FunctionalInterface
interface Converter<F, T> {
    T convert(F from);
} 

 public void functionalInterfaceExample(){

          //Functional Interface
        Converter<String, Integer> converter = (value)->Integer.valueOf(value);
        Integer convertedValue = converter.convert("3838");
        System.out.println(convertedValue);
}

 //TimeZones : import java.time.*; to get all API's
public void showTimeZones(){
        System.out.println(ZoneId.getAvailableZoneIds());
        // prints all available timezone ids
       
        ZoneId zone1 = ZoneId.of("Europe/Berlin");
        ZoneId zone2 = ZoneId.of("Brazil/East");
        System.out.println(zone1.getRules());
        System.out.println(zone2.getRules());
}

//Date & Time API
public void showDateTime(){
       //Clock
        Clock clock = Clock.systemDefaultZone();
        long millis = clock.millis();
       
        Instant instant = clock.instant();
        Date legacyDate = Date.from(instant);   // legacy java.util.Date
       
        System.out.println("millis :"+millis);
        System.out.println("instant ::"+ instant);
        System.out.println("legacyDate ::"+ legacyDate);
}