Check if a particular value exists in Java LinkedHashMap

LinkedHashMap is a class in Java that implements the Map interface. It uses a doubly linked list to maintain the insertion order of elements. So, when we loop through a LinkedHashMap, the elements will be returned in the order we had inserted them.

The given task is to check if a particular value exists in a LinkedHashMap in Java. Let's look at some scenarios to understand the problem better:

Scenario

Input: {1=Mikasa, 2=Eren, 3=Reiner}, Value to check: Mikasa Output: Value Exists Explanation: The LinkedHashMap has the value that we are looking for.

Checking if a Value Exists in LinkedHashMap

The following are the ways we can check if a particular value exists in a LinkedHashMap in Java:

• Using containsValue() Method
• Using entrySet() Method
• Using Stream API

Using containsValue() Method

The containsValue() method is from the Map interface, which is implemented by the LinkedHashMap class. This method is used to check if a particular value exists in the LinkedHashMap. If the value exists, it returns TRUE; otherwise, it returns FALSE.

Syntax

Following is the syntax of the containsValue() method:

map.containsValue(value);

The following are the parameters:

• map is the object we create of the LinkedHashMap class
• value is the value we want to check.

Example

In the following example, we are searching for a particular value in a LinkedHashMap  using the containsValue() method:

import java.util.LinkedHashMap; public class CheckIfValueExists { public static void main(String[] args){ LinkedHashMap<Integer, String> map = new LinkedHashMap<>(); map.put(1, "Kisaki"); map.put(2, "Takemichi"); map.put(3, "Mikey"); map.put(4, "Draken"); String valueToCheck = "Mikey"; if(map.containsValue(valueToCheck)) { System.out.println("Value exists in the LinkedHashMap" + " and that is: " + valueToCheck); } else { System.out.println("Value does not exist in the LinkedHashMap"); } } }

When you run the above code, it will produce the following output:

Value exists in the LinkedHashMap and it is: Mikey 

Using entrySet() Method

The entrySet() is another method from the Map Interface. This method returns a Set view (set of key-value pairs) of the mappings in the LinkedHashMap. We can get the set view and then use the contains() method of the Set interface to check if a particular value exists in the LinkedHashMap.

Syntax

map.entrySet();

The following are the parameters of this function:

• map is the object we create of the LinkedHashMap class
• entrySet is the set view of the mappings in the LinkedHashMap.

Example

In the following example, we are retrieving the SetView object of a LinkedHashMap, comparing the value of each key in it with the key we are searching for:

import java.util.LinkedHashMap; import java.util.Map; import java.util.Set; public class CheckIfValueExists { public static void main(String[] args){ LinkedHashMap<Integer, Integer> map = new LinkedHashMap<>(); map.put(1, 2); map.put(2, 3); map.put(3, 4); map.put(4, 5); int valueToCheck = 3; int key = 2; Set<Map.Entry<Integer, Integer>> entrySet = map.entrySet(); boolean exists = false; for(Map.Entry<Integer, Integer> entry : entrySet) { if(entry.getValue() == valueToCheck) { exists = true; key = entry.getKey(); break; } } if(exists) { System.out.println("The value " + valueToCheck + " exists in the LinkedHashMap with key: " + key); } else { System.out.println("Value does not exist in the LinkedHashMap"); } } }

When you run the above code, it will produce the following output:

The value 3 exists in the LinkedHashMap with key: 2 

Using Stream API

Stream API in Java allows us to perform functional-style operations on collections. Functional-style uses lambda expressions to process data. We have methods in the Stream API, and we can chain them together to get the result. You can search for a value in a LinkedHashMap using the streams API as shown below:

map.entrySet().stream().anyMatch(entry -> entry.getKey().equals(key) && !entry.getValue()); 

Let's break down the above snippet:

• map is the object we create of the LinkedHashMap class
• entrySet() returns a set view of the mappings contained in the map, as we saw in the previous section.
• stream() converts the set view to a Stream.
• anyMatch() is a terminal operation that returns true if any elements of the stream match the provided predicate.
• entry is a Map.Entry object that represents a key-value pair in the map.
• entry.getKey() returns the key of the entry.
• entry.getValue() returns the value of the entry.

Example

In the below example, first we will create a LinkedHashMap of String and Boolean, where each key is the name of a person and the value is a boolean indicating whether that person is available or not.

• Next, we will make a stream of the map entries using the entrySet().stream() method.
• Then we will use the anyMatch() method to check if the specified person exists in the map and is available (i.e., the value is true).
• Then we will print the result based on the value of the boolean variable.
  

import java.util.LinkedHashMap; public class CheckIfValueExists { public static void main(String[] args){ LinkedHashMap<String, Boolean> map = new LinkedHashMap<>(); map.put("Zoro", false); map.put("Luffy", true); map.put("Nami", true); map.put("Ussop", false); map.put("Sanji", true); String key = "Nami"; // Check if the person is in the map and is not available boolean isAvailable = map.entrySet().stream() .anyMatch(entry -> entry.getKey().equals(key) && entry.getValue()); if(isAvailable) { System.out.println(key + " is available."); } else { System.out.println(key + " is not available."); } } }

When you run the above code, it will produce the following output:

Nami is available.