Programming

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Lambdas / Static Methods

STATIC METHODS

Java 8 allows static methods in interfaces. 
 
/**
 * Static methods are allowed in interfaces (Java 8)
 * It's always better to put related methods in the same place
 */

package com.minte9.lambdas.static_methods;
import java.util.function.BinaryOperator;
import java.util.stream.Stream;
import static org.junit.Assert.assertEquals;

public class StaticMethod {
  public static void main(String[] args) {
      
    int a = MyStream.of(1, 2, 3)
      .reduce(0, (acc, x) -> acc + x) // addition
    ;

    int b = MyStream.of(1, 2, 3)
      .reduce(0, (acc, x) -> acc - x) // substraction
    ;

    assertEquals(a, 6);
    assertEquals(b, -6);
    
    System.out.println("Tests passed");
  }
}

abstract interface MyStream<T> extends Stream<T> {
  
    @SafeVarargs 
    @SuppressWarnings("varargs")

    static <T> Stream<T> of(T... values) { // Look Here
        return Stream.of(values);
    }

    abstract T reduce(T arg0, BinaryOperator<T> arg1);
}

Method Reference

The syntax when lambdas call methods on its parameter is named method reference. 
 
/**
 * Method reference
 * 
 * Use a lambdas that call methods on its parameter
 * Standard form of method reference is ClassName::methodName
 * The code is not only more shorter, also a lot easier to read
 */
package com.minte9.lambdas.static_methods;

import java.util.Arrays;
import java.util.List;

public class MethodReference {
  public static void main(String[] args) {
      
    List<String> myList = Arrays.asList("a", "b", "c");

    myList.stream()
      .map(x -> x + x)
      .map(String::toUpperCase)
      .forEach(System.out::println); // AA BB CC
  }
}




References


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