How to Set a Default Value for a Key in a Map in Java - Step by Step Examples

How to Set a Default Value for a Key in a Map in Java ?

Answer

To set a default value for a key in a map in Java, you can use the computeIfAbsent method.

✐ Examples

1 Setting a Default Value Using computeIfAbsent Method

We can set a default value for a key in a map in Java using the computeIfAbsent method, which inserts a key-value pair if the key does not already exist in the map.

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 computeIfAbsent method to set a default value for a key. The computeIfAbsent method takes the key and a function that returns the default value to be inserted if the key is not already present in the map.
We print the updated map to the console using a for-each loop and 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");

        // Set a default value using computeIfAbsent method
        myMap.computeIfAbsent(4, k -> "default");

        // Print the updated map
        for (Map.Entry<Integer, String> entry : myMap.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}

Output

1: one
2: two
3: three
4: default

2 Setting Multiple Default Values Using computeIfAbsent Method

We can set multiple default values for keys in a map in Java using the computeIfAbsent method, which inserts key-value pairs if the keys do not already exist in the map.

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 computeIfAbsent method to set multiple default values for keys. The computeIfAbsent method takes the key and a function that returns the default value to be inserted if the key is not already present in the map.
We print the updated map to the console using a for-each loop and 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");

        // Set multiple default values using computeIfAbsent method
        myMap.computeIfAbsent(4, k -> "default");
        myMap.computeIfAbsent(5, k -> "default");

        // Print the updated map
        for (Map.Entry<Integer, String> entry : myMap.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}

Output

1: one
2: two
3: three
4: default
5: default

3 Setting a Default Value Conditionally Using putIfAbsent Method

We can set a default value for a key in a map in Java using the putIfAbsent method, which inserts a key-value pair if the key does not already exist in the map, based on a condition.

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 putIfAbsent method to set a default value for a key based on a condition. The putIfAbsent method takes the key and the value to be inserted if the key is not already present in the map.
We print the updated map to the console using a for-each loop and 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");

        // Set a default value conditionally using putIfAbsent method
        myMap.putIfAbsent(4, "default");

        // Print the updated map
        for (Map.Entry<Integer, String> entry : myMap.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}

Output

1: one
2: two
3: three
4: default

Summary

In this tutorial, we learned How to Set a Default Value for a Key in a Map in Java language with well detailed examples.

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How to Set a Default Value for a Key in a Map in Java - Step by Step Examples