Java8 中使用forEach + lambda expression/method reference 循环List和Map

Reference: http://www.mkyong.com/java8/java-8-foreach-examples/

/*
 Java8 中使用forEach + lambda expression/method reference 循环列表
 */

import java.util.ArrayList;
import java.util.List;

public class Exercise {
  
  public static void main(String args[]) {
    List items = new ArrayList<>();
    items.add("A");
    items.add("B");
    items.add("C");
    // Normal for-loop to loop a list
    for (String item: items){
      System.out.println(item);
    }
    // lambda expression
    // output A B C
    items.forEach(item -> System.out.println(item));
    // output C
    items.forEach(item -> {
      if ("C".equals(item)){
        System.out.println(item);
      }
    });

    // method reference
    // output A B C (color red)
    items.forEach(System.err::println);

    // Stream and filter
    // output B
    items.stream().filter(s -> s.contains("B")).
        forEach(System.out::println);
  }

}

/*
 Java8 中使用forEach + lambda expression/method reference 循环Map
 */

import java.util.HashMap;
import java.util.Map;

public class Exercise {
  
  public static void main(String args[]) {
    Map items = new HashMap<>();
    items.put("A", 10);
    items.put("B", 20);
    items.put("C", 30);
    items.put("D", 60);
    // normal for loop
    System.out.println("Normal for loop: ");
    for (Map.Entry entry : items.entrySet()) {
      System.out.println("Item: " + entry.getKey() +"\t"+ "Count: " + entry.getValue());
    }
    // In Java8, we can loop a Map with forEach + lambda expression
    System.out.println("forEach + lambda expression: ");
    items.forEach((k, v) -> System.out.println("Item: " + k +"\t"+ "Count: " + v));
    // witr if condition
    System.out.println("If condition");
    items.forEach((k, v) -> {
      if ("A".equals(k)) {
        System.out.println(k);
      }
    });
  }

}