Implement Key Value Pair in Java

  2. HowTo
  3. Java Howtos
  4. Implement Key Value Pair in Java
Mohammad Irfan Jan 30, 2023 Mar 12, 2021
Java Java Collection
  1. Implement Key Value Pair Using HashMap in Java
  2. Implement Key Value Pair Using the Map.Entry in Java
  3. Implement Key Value Pair Using the AbstractMap.SimpleEntry Class in Java
  4. Implement Key Value Pair Using Map.entry in Java
  5. Implement Key Value Pair Using AbstractMap.SimpleImmutableEntry in Java
  6. Implement Key Value Pair Using Maps.immutableEntry in Java
  7. Implement Key Value Pair Using Properties Class in Java
Implement Key Value Pair in Java

This tutorial introduces how to implement key-value pairs in Java.

In Java, to deal with the key-value pair, the Map interface and its implementation classes are used. We can use classes such as HashMap and TreeMap to store data into the key-value pair. Apart from these built-in classes, we can create our own class that can hold the key-value pair.

Here, we will use HashMap, user-defined class, AbstractMap, Map.entry(), AbstractMap.SimpleImmutableEntry() and Properties, etc. Let’s take a close look at the examples.

Implement Key Value Pair Using HashMap in Java

Java’s Map interface in the Collection framework can be used to store data into the key-value pair. Here, we use the HashMap class to store string type key-value pairs. See the example below.

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

public class SimpleTesting extends Thread{
	public static void main(String[] args) {
		Map<String, String> map = new HashMap<>();
		map.put("name", "Rohan");
		map.put("sname", "Kumar");
		System.out.println(map);
	}
}

Output:

{sname=Kumar, name=Rohan}

Implement Key Value Pair Using the Map.Entry in Java

Here, we use the Map.Entry interface to create a custom class that will hold data in key-value pairs. We create a class, Student, with two instance variables to hold key and value pair. We also created getters and setters methods to set values for each instance of this class. See the example below.

import java.util.Map;
class Student<K, V> implements Map.Entry<K, V> {
    private final K key;
    private V value;

    public Student(K key, V value) {
        this.key = key;
        this.value = value;
    }
    @Override
    public K getKey() {
        return key;
    }
    @Override
    public V getValue() {
        return value;
    }
    @Override
    public V setValue(V value) {
        V old = this.value;
        this.value = value;
        return old;
    }
}
public class SimpleTesting extends Thread{
    public static void main(String[] args) {
        Student<String, String> student = new Student<>("name","Rohan");
        String key = student.getKey();
        String value = student.getValue();
        System.out.println("{"+key+":"+value+"}");
    }  
}

Output:

{name:Rohan}

Implement Key Value Pair Using the AbstractMap.SimpleEntry Class in Java

Here, we use the AbstractMap class to implement key-value pair. The getKey() and getValue() methods are used to get key and value respectively. See the below example.

import java.util.AbstractMap;
import java.util.Map;

public class SimpleTesting extends Thread{
    public static void main(String[] args) {
        Map.Entry<String,String> entry =
                new AbstractMap.SimpleEntry<String, String>("name", "Rohan");
        String key = entry.getKey();
        String value = entry.getValue();
        System.out.println("{"+key+":"+value+"}");
    }  
}

Output:

{name:Rohan}

Implement Key Value Pair Using Map.entry in Java

We can use Map.entry to store data into key and value pair. Here, we use the Entry interface and its methods getKey() and getValue() to get key and value respectively. See the below example.

import java.util.Map;
import java.util.Map.Entry;
public class SimpleTesting extends Thread{
    public static void main(String[] args) {
        Entry<String, String> entry = Map.entry("name", "Rohan");
        String key = entry.getKey();
        String value = entry.getValue();
        System.out.println("{"+key+":"+value+"}");
    }  
}

Output:

{name:Rohan}

Implement Key Value Pair Using AbstractMap.SimpleImmutableEntry in Java

We can use SimpleImmutableEntry to create an immutable set of key-value pairs. See the below example.

import java.util.AbstractMap;
import java.util.Map.Entry;
public class SimpleTesting extends Thread{
    public static void main(String[] args) {
        Entry<String, String> entry = new AbstractMap.SimpleImmutableEntry<>("name","Rohan");
        String key = entry.getKey();
        String value = entry.getValue();
        System.out.println("{"+key+":"+value+"}");
    }  
}

Output:

{name:Rohan}

Implement Key Value Pair Using Maps.immutableEntry in Java

Here, we use Map.immutableEntry to create key-value pair in Java. We use getKey() and getValue() methods to get key and value respectively.

import java.util.AbstractMap;
import java.util.Map;
import java.util.Map.Entry;

import com.google.common.collect.Maps;
public class MainClass extends Thread{
    public static void main(String[] args) {
        Map.Entry<String, String> entry = Maps.immutableEntry("name", "Rohan");
        String key = entry.getKey();
        String value = entry.getValue();
        System.out.println("{"+key+":"+value+"}");
    }  
}

Output:

{name:Rohan}

Implement Key Value Pair Using Properties Class in Java

The Properties class of Java collections can be used to store data into key-value pairs. The getProperty() method of the Properties class returns the value associated with the key. See the below example.

import java.util.Properties;    
public class MainClass extends Thread{
    public static void main(String[] args) {
        Properties props = new Properties();
        props.setProperty("name", "Rohan"); // (key, value)
        String value = props.getProperty("name");
        System.out.println("{name:"+value+"}");
    }  
}

Output:

{name:Rohan}

Related Article - Java Collection