How to Check if a Key Exists in a Map in Java - Step by Step Examples

How to Check if a Key Exists in a Map in Java ?

Answer

To check if a key exists in a map in Java, you can use the containsKey method. This method returns a boolean value indicating whether the map contains the specified key.

✐ Examples

1 Checking if a Key Exists Using containsKey Method

We can check if a key exists in a map in Java using the containsKey method, which returns true if the map contains the specified key and false otherwise.

For example,

We start by importing the java.util.HashMap package, which provides the HashMap class needed to create and manipulate the map.
We declare and initialize a map named myMap with some key-value pairs. In this example, the map has integer keys and string values.
We use the containsKey method to check for a specific key in the map. The containsKey method returns a boolean value indicating whether the map contains the specified key.
We print the result to the console using System.out.println.

Java Program

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

public class Main {
    public static void main(String[] args) {
        // Declare and initialize a map
        Map<Integer, String> myMap = new HashMap<>();
        myMap.put(1, "one");
        myMap.put(2, "two");
        myMap.put(3, "three");

        // Check if a key exists using containsKey method
        boolean keyExists = myMap.containsKey(2);

        // Print the result
        System.out.println("Does key 2 exist? " + keyExists);
    }
}

Output

Does key 2 exist? true

2 Checking if a Key Does Not Exist Using containsKey Method

We can check if a key does not exist in a map in Java using the containsKey method, which returns false if the map does not contain the specified key.

For example,

We start by importing the java.util.HashMap package, which provides the HashMap class needed to create and manipulate the map.
We declare and initialize a map named myMap with some key-value pairs. In this example, the map has integer keys and string values.
We use the containsKey method to check for a specific key in the map. The containsKey method returns a boolean value indicating whether the map contains the specified key.
We print the result to the console using System.out.println.

Java Program

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

public class Main {
    public static void main(String[] args) {
        // Declare and initialize a map
        Map<Integer, String> myMap = new HashMap<>();
        myMap.put(1, "one");
        myMap.put(2, "two");
        myMap.put(3, "three");

        // Check if a key does not exist using containsKey method
        boolean keyExists = myMap.containsKey(4);

        // Print the result
        System.out.println("Does key 4 exist? " + keyExists);
    }
}

Output

Does key 4 exist? false

3 Checking Multiple Keys Using containsKey Method

We can check if multiple keys exist in a map in Java using the containsKey method, which returns true if the map contains the specified key and false otherwise.

For example,

We start by importing the java.util.HashMap package, which provides the HashMap class needed to create and manipulate the map.
We declare and initialize a map named myMap with some key-value pairs. In this example, the map has integer keys and string values.
We use the containsKey method to check for multiple keys in the map. The containsKey method returns a boolean value indicating whether the map contains the specified key.
We print the results to the console using System.out.println.

Java Program

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

public class Main {
    public static void main(String[] args) {
        // Declare and initialize a map
        Map<Integer, String> myMap = new HashMap<>();
        myMap.put(1, "one");
        myMap.put(2, "two");
        myMap.put(3, "three");

        // Check if multiple keys exist using containsKey method
        boolean keyExistsOne = myMap.containsKey(1);
        boolean keyExistsFour = myMap.containsKey(4);

        // Print the results
        System.out.println("Does key 1 exist? " + keyExistsOne);
        System.out.println("Does key 4 exist? " + keyExistsFour);
    }
}

Output

Does key 1 exist? true
Does key 4 exist? false

Summary

In this tutorial, we learned How to Check if a Key Exists in a Map in Java language with well detailed examples.

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How to Check if a Key Exists in a Map in Java - Step by Step Examples