Java TreeMap containsKey() Method

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Description

The Java TreeMap containsKey(Object key) method is used to return 'true' if this map contains a mapping for the specified key.

Declaration

Following is the declaration for java.util.TreeMap.containsKey() method.

public boolean containsKey(Object key)

Parameters

key − This is the key whose presence in this map is to be tested.

Return Value

The method call returns true if this map contains a mapping for the specified key.

Exception

• ClassCastException − This is thrown if the specified key cannot be compared with the keys currently in the map.

• NullPointerException − This is thrown if the specified key is null and this map uses natural ordering, or its comparator does not permit null keys.

Checking a Key to Exist in a TreeMap of Integer,Integer Pairs Example

The following example shows the usage of Java TreeMap containsKey() method to check if a key is present in a map or not. We've created a TreeMap object of Integer,Integer pairs. Then few entries are added to map and using containsKey() we're checking if key is present and then printing the same.

package com.tutorialspoint;

import java.util.TreeMap;

public class TreeMapDemo {
   public static void main(String[] args) {
      
      // creating tree map 
      TreeMap<Integer, Integer> treemap = new TreeMap<>();

      // populating tree map
      treemap.put(2, 2);
      treemap.put(1, 1);
      treemap.put(3, 3);
      treemap.put(6, 6);
      treemap.put(5, 5);

      System.out.println("Checking key value 6");
      System.out.println("Value for key 6 exists: "+ treemap.containsKey(6));
   }    
}

Output

Let us compile and run the above program, this will produce the following result.

Checking key value 6
Value for key 6 exists: true

Checking a Key to Exist in a TreeMap of Integer,String Pairs Example

The following example shows the usage of Java TreeMap containsKey() method to check if a key is present in a map or not. We've created a TreeMap object of Integer,String pairs. Then few entries are added to map and using containsKey() we're checking if key is present and then printing the same.

package com.tutorialspoint;

import java.util.TreeMap;

public class TreeMapDemo {
   public static void main(String[] args) {
      
      // creating tree map 
      TreeMap<Integer, String> treemap = new TreeMap<>();

      // populating tree map
      treemap.put(2, "two");
      treemap.put(1, "one");
      treemap.put(3, "three");
      treemap.put(6, "six");
      treemap.put(5, "five");

      System.out.println("Checking key value 6");
      System.out.println("Value for key 6 exists: "+ treemap.containsKey(6));
   }    
}

Output

Let us compile and run the above program, this will produce the following result.

Checking key value 6
Value for key 6 exists: true

Checking a Key to Exist in a TreeMap of Integer,Object Pairs Example

The following example shows the usage of Java TreeMap containsKey() method to check if a key is present in a map or not. We've created a TreeMap object of Integer,Studet pairs. Then few entries are added to map and using containsKey() we're checking if key is present and then printing the same.

package com.tutorialspoint;

import java.util.TreeMap;

public class TreeMapDemo {
   public static void main(String[] args) {
      
      // creating tree map 
      TreeMap<Integer, Student> treemap = new TreeMap<>();

      // populating tree map
      treemap.put(2, new Student(2, "Robert"));
      treemap.put(1, new Student(1, "Julie"));  
      treemap.put(3, new Student(3, "Adam"));
      treemap.put(6, new Student(6, "Julia"));
      treemap.put(5, new Student(5, "Tom"));

      System.out.println("Checking key value 6");
      System.out.println("Value for key 6 exists: "+ treemap.containsKey(6));
   }    
}
class Student {
   int rollNo;
   String name;

   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }

   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
   @Override
   public boolean equals(Object obj) {
      if(obj == null) return false;
      Student s = (Student)obj;
      return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name);
   }
}

Output

Let us compile and run the above program, this will produce the following result.

Checking key value 6
Value for key 6 exists: true