HashMap
Each element in a Map is actually two objects, a key and a value.
/**
* In a HashMap you can have duplicate values ...
* but no duplicate keys.
*/
package com.minte9.collections.maps;
import java.util.HashMap;
public class Hashmaps {
public static void main(String[] args) {
HashMap<String, Integer> scores =
new HashMap<String, Integer>();
scores.put("a", 1);
scores.put("a", 2); // overrites "a" key
scores.put("b", 2);
scores.put("c", 2);
System.out.println(scores); // {a=2, b=2, c=2}
System.out.println(
scores.get("a") // 2
);
}
}
Loop
If you only need the values, use for loop and values().
/**
* To parse a HashMap use for loop with ...
*
* keySet(), if you need only the keys,
* values(), if you need only the values,
* entrySet(), if you need both.
*/
package com.minte9.collections.maps;
import java.util.HashMap;
import java.util.Map;
public class Loops {
public static void main(String[] args) {
HashMap<String, Integer> scores =
new HashMap<String, Integer>();
scores.put("a", 1);
scores.put("b", 2);
scores.put("c", 3);
for (String key : scores.keySet()) {
System.out.println(key);
// a b c
}
for(Object value : scores.values()) {
System.out.println(value);
// 1 2 3
}
for(Map.Entry<String, Integer> entry : scores.entrySet()) {
String key = entry.getKey();
Integer value = entry.getValue();
System.out.println(key + value);
// a1 b2 c3
}
}
}
Last update: 531 days ago
