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Java TreeMap containsKey() Method

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

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

public boolean containsKey(Object key)

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

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

• 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.

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));
   }    
}

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

Checking key value 6
Value for key 6 exists: true

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));
   }    
}

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

Checking key value 6
Value for key 6 exists: true

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);
   }
}

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

Checking key value 6
Value for key 6 exists: true

java_util_treemap.htm

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