Java TreeMap put() Method

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Description

The Java TreeMap put(K key,V value) method is used to associate the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replaced.

Declaration

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

public V put(K key,V value)

Parameters

• key − This is the key with which the specified value is to be associated.

• value − This is the value to be associated with the specified key.

Return Value

The method call returns the previous value associated with key, or null if there was no mapping for key.

Exception

NA

Adding a Key-Value Entry to a TreeMap of Integer,Integer Pair Example

The following example shows the usage of Java TreeMap put() method to add/update a key-value mapping in this map. We've created a TreeMap object of Integer,Integer pairs. Then few entries are added using put() method, map is printed then using put() we're updating a value for a key and map is printed again to see the effect of updating an entry.

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);   

      // Putting value at key 3
      System.out.println("Value before modification: "+ treemap);            
      System.out.println("Value returned: "+ treemap.put(3,7));      
      System.out.println("Value after modification: "+ treemap);
   }     
}

Output

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

Value before modification: {1=1, 2=2, 3=3, 5=5, 6=6}
Value returned: 3
Value after modification: {1=1, 2=2, 3=7, 5=5, 6=6}

Adding a Key-Value Entry to a TreeMap of Integer,String Pair Example

The following example shows the usage of Java TreeMap put() method to add/update a key-value mapping in this map. We've created a TreeMap object of Integer,String pairs. Then few entries are added using put() method, map is printed then using put() we're updating a value for a key and map is printed again to see the effect of updating an entry.

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");   

      // Putting value at key 3
      System.out.println("Value before modification: "+ treemap);            
      System.out.println("Value returned: "+ treemap.put(3,"TP"));      
      System.out.println("Value after modification: "+ treemap);
   }     
}

Output

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

Value before modification: {1=one, 2=two, 3=three, 5=five, 6=six}
Value returned: three
Value after modification: {1=one, 2=two, 3=TP, 5=five, 6=six}

Adding a Key-Value Entry to a TreeMap of Integer,Object Pair Example

The following example shows the usage of Java TreeMap put() method to add/update a key-value mapping in this map. We've created a TreeMap object of Integer,Student pairs. Then few entries are added using put() method, map is printed then using put() we're updating a value for a key and map is printed again to see the effect of updating an entry.

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")); 

      // Putting value at key 3
      System.out.println("Value before modification: "+ treemap);            
      System.out.println("Value returned: "+ treemap.put(3, new Student(7, "Alfred")));     
      System.out.println("Value after modification: "+ treemap);
   }     
}
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.

Value before modification: {1=[ 1, Julie ], 2=[ 2, Robert ], 3=[ 3, Adam ], 5=[ 5, Tom ], 6=[ 6, Julia ]}
Value returned: [ 3, Adam ]
Value after modification: {1=[ 1, Julie ], 2=[ 2, Robert ], 3=[ 7, Alfred ], 5=[ 5, Tom ], 6=[ 6, Julia ]}