Java Map set new value computed from Lambda expression

Description

Java Map set new value computed from Lambda expression 


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

public class Main {
  public static void main(String[] args) {
    Map<Integer, String> map = new HashMap<>();

    for (int i = 0; i < 10; i++) {
      map.put(i, "Value " + i);
    }//from  w w w.  j  a va 2  s  .  c o  m
    System.out.println(map);
    
    map.forEach((id, val) -> System.out.println(val));
    
    map.computeIfPresent(3, (num, val) -> "combined:"+val +" "+ num);
    
    System.out.println(map);
    
    System.out.println(map.get(3));
    System.out.println(map.get(2));
    
  }
}

Set null to computed value 


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

public class Main {
  public static void main(String[] args) {
    Map<Integer, String> map = new HashMap<>();

    for (int i = 0; i < 10; i++) {
      map.put(i, "Value " + i);
    }//from   ww  w  .j a  v a2s . c o m
    System.out.println(map);
    
    map.forEach((id, val) -> System.out.println(val));
    
    map.computeIfPresent(3, (num, val) -> "combined:"+val +" "+ num);
    
    System.out.println(map);
    
    map.computeIfPresent(3, (num, val) -> null);
    System.out.println(map);
    System.out.println(map.containsKey(3));     // false
    
  }
}

Set new value if absent 


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

public class Main {
  public static void main(String[] args) {
    Map<Integer, String> map = new HashMap<>();

    for (int i = 0; i < 10; i++) {
      map.put(i, "Value " + i);
    }//www.j av  a  2  s .c  om
    System.out.println(map);
    
    map.forEach((id, val) -> System.out.println(val));
    
    map.computeIfPresent(3, (num, val) -> "combined:"+val +" "+ num);
    
    System.out.println(map);
    
    map.computeIfPresent(3, (num, val) -> null);
    System.out.println(map);
    System.out.println(map.containsKey(3));     // false
    
    map.computeIfAbsent(3, num -> "new");
    
    System.out.println(map);
    System.out.println(map.containsKey(3));     // true
    
  }
}



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