TreeMap is a part of the Java Collections Framework and provides an implementation of the NavigableMap interface. It is used to store key-value pairs in a sorted order, based on the natural ordering of its keys or by a custom comparator. This tutorial will cover all methods of TreeMap with examples and outputs, highlighting key points, use cases, best practices, performance considerations, and a real-time example with CRUD operations.

Introduction
Key Points
TreeMap Methods
- put()
- putAll()
- get()
- remove()
- clear()
- size()
- isEmpty()
- containsKey()
- containsValue()
- keySet()
- values()
- entrySet()
- firstKey()
- lastKey()
- lowerKey()
- higherKey()
- floorKey()
- ceilingKey()
- pollFirstEntry()
- pollLastEntry()
- forEach()
- replace()
- compute()
- computeIfAbsent()
- computeIfPresent()
- merge()
Use Cases
Best Practices
Performance Considerations
Real-time Example with CRUD Operations
Conclusion

1. Introduction

A TreeMap in Java is a part of the Java Collections Framework and provides a way to manage key-value pairs in a sorted order. It is found in the java.util package and is backed by a TreeMap, ensuring that elements are stored in ascending order based on the natural ordering of the keys or by a custom comparator provided at map creation time.

2. Key Points

TreeMap allows null values but does not allow null keys.
It maintains elements in ascending order based on the natural ordering of keys or a custom comparator.
It is not synchronized.
It provides logarithmic time performance for basic operations like put, get, and remove.

3. TreeMap Methods

3.1. put()

The put() method is used to insert key-value pairs into the TreeMap.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        System.out.println(fruits);
    }
}

Output:

{Apple=50, Banana=30, Mango=20}

3.2. putAll()

The putAll() method adds all key-value pairs from another map to the TreeMap.

Example:

import java.util.TreeMap;
import java.util.Map;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);

        Map<String, Integer> moreFruits = new TreeMap<>();
        moreFruits.put("Mango", 20);
        moreFruits.put("Orange", 40);

        fruits.putAll(moreFruits);
        System.out.println(fruits);
    }
}

Output:

{Apple=50, Banana=30, Mango=20, Orange=40}

3.3. get()

The get() method retrieves the value associated with the specified key.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        System.out.println(fruits.get("Banana")); // 30
    }
}

Output:

3.4. remove()

The remove() method removes the key-value pair associated with the specified key.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        fruits.remove("Banana");
        System.out.println(fruits); // {Apple=50, Mango=20}
    }
}

Output:

{Apple=50, Mango=20}

3.5. clear()

The clear() method removes all key-value pairs from the TreeMap.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        fruits.clear();
        System.out.println(fruits); // {}
    }
}

Output: ``{}


### 3.6. size()
The `size()` method returns the number of key-value pairs in the `TreeMap`.

**Example:**
```java
import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        System.out.println(fruits.size()); // 3
    }
}

Output:

3.7. isEmpty()

The isEmpty() method checks if the TreeMap is empty.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        System.out.println(fruits.isEmpty()); // true
        fruits.put("Apple", 50);
        System.out.println(fruits.isEmpty()); // false
    }
}

Output:

true
false

3.8. containsKey()

The containsKey() method checks if the TreeMap contains a specified key.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        System.out.println(fruits.containsKey("Banana")); // true
        System.out.println(fruits.containsKey("Mango")); // false
    }
}

Output:

true
false

3.9. containsValue()

The containsValue() method checks if the TreeMap contains a specified value.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        System.out.println(fruits.containsValue(30)); // true
        System.out.println(fruits.containsValue(20)); // false
    }
}

Output:

true
false

3.10. keySet()

The keySet() method returns a set view of the keys contained in the TreeMap.

Example:

import java.util.TreeMap;
import java.util.Set;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        Set<String> keys = fruits.keySet();
        System.out.println(keys); // [Apple, Banana, Mango]
    }
}

Output:

[Apple, Banana, Mango]

3.11. values()

The values() method returns a collection view of the values contained in the TreeMap.

Example:

import java.util.TreeMap;
import java.util.Collection;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        Collection<Integer> values = fruits.values();
        System.out.println(values); // [50, 30, 20]
    }
}

Output:

[50, 30, 20]

3.12. entrySet()

The entrySet() method returns a set view of the mappings contained in the TreeMap.

Example:

import java.util.TreeMap;
import java.util.Set;
import java.util.Map.Entry;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        Set<Entry<String, Integer>> entries = fruits.entry

Set();
        for (Entry<String, Integer> entry : entries) {
            System.out.println(entry.getKey() + " = " + entry.getValue());
        }
    }
}

Output:

Apple = 50
Banana = 30
Mango = 20

3.13. firstKey()

The firstKey() method returns the first (lowest) key currently in the TreeMap.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        System.out.println(fruits.firstKey()); // Apple
    }
}

Output:

Apple

3.14. lastKey()

The lastKey() method returns the last (highest) key currently in the TreeMap.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        System.out.println(fruits.lastKey()); // Mango
    }
}

Output:

Mango

3.15. lowerKey()

The lowerKey() method returns the greatest key strictly less than the given key, or null if there is no such key.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        System.out.println(fruits.lowerKey("Banana")); // Apple
    }
}

Output:

Apple

3.16. higherKey()

The higherKey() method returns the least key strictly greater than the given key, or null if there is no such key.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        System.out.println(fruits.higherKey("Banana")); // Mango
    }
}

Output:

Mango

3.17. floorKey()

The floorKey() method returns the greatest key less than or equal to the given key, or null if there is no such key.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        System.out.println(fruits.floorKey("Banana")); // Banana
    }
}

Output:

Banana

3.18. ceilingKey()

The ceilingKey() method returns the least key greater than or equal to the given key, or null if there is no such key.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        System.out.println(fruits.ceilingKey("Banana")); // Banana
    }
}

Output:

Banana

3.19. pollFirstEntry()

The pollFirstEntry() method removes and returns a key-value mapping associated with the least key in this map, or null if the map is empty.

Example:

import java.util.TreeMap;
import java.util.Map.Entry;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        Entry<String, Integer> firstEntry = fruits.pollFirstEntry();
        System.out.println(firstEntry); // Apple=50
        System.out.println(fruits); // {Banana=30, Mango=20}
    }
}

Output:

Apple=50
{Banana=30, Mango=20}

3.20. pollLastEntry()

The pollLastEntry() method removes and returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.

Example:

import java.util.TreeMap;
import java.util.Map.Entry;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        Entry<String, Integer> lastEntry = fruits.pollLastEntry();
        System.out.println(lastEntry); // Mango=20
        System.out.println(fruits); // {Apple=50, Banana=30}
    }
}

Output:

Mango=20
{Apple=50, Banana=30}

3.21. forEach()

The forEach() method performs the given action for each entry in the TreeMap.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.put("Mango", 20);
        fruits.forEach((key, value) -> System.out.println(key + " = " + value));
    }
}

Output:

Apple = 50
Banana = 30
Mango = 20

3.22. replace()

The replace() method replaces the entry for the specified key only if it is currently mapped to some value.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.replace("Banana", 40);
        System.out.println(fruits); // {Apple=50, Banana=40, Mango=20}
    }
}

Output:

{Apple=50, Banana=40, Mango=20}

3.23. compute()

The compute() method computes a new mapping for the specified key and its current mapped value (or null if there is no current mapping).

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.compute("Banana", (key, value) -> (value == null) ? 40 : value + 10);
        System.out.println(fruits); // {Apple=50, Banana=40, Mango=20}
    }
}

Output:

{Apple=50, Banana=40, Mango=20}

3.24. computeIfAbsent()

The computeIfAbsent() method computes a mapping for the specified key if it is not already present.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.computeIfAbsent("Mango", key -> 20);
        System.out.println(fruits); // {Apple=50, Banana=30, Mango=20}
    }
}

Output:

{Apple=50, Banana=30, Mango=20}

3.25. computeIfPresent()

The computeIfPresent() method computes a new mapping for the specified key if it is currently present.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.computeIfPresent("Banana", (key, value) -> value + 10);
        System.out.println(fruits); // {Apple=50, Banana=40, Mango=20}
    }
}

Output:

{Apple=50, Banana=40, Mango=20}

3.26. merge()

The merge() method merges the

specified value with the existing value associated with the specified key.

Example:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Integer> fruits = new TreeMap<>();
        fruits.put("Apple", 50);
        fruits.put("Banana", 30);
        fruits.merge("Banana", 20, (oldValue, newValue) -> oldValue + newValue);
        System.out.println(fruits); // {Apple=50, Banana=50, Mango=20}
    }
}

Output:

{Apple=50, Banana=50, Mango=20}

4. Use Cases

Sorted collections: Storing key-value pairs in a sorted order based on keys.
Database representation: Representing tables with rows as key-value pairs with natural order.
Configuration settings: Storing application settings as key-value pairs with natural order.

5. Best Practices

Use appropriate initial capacity: If the size of the map is known in advance, setting an initial capacity can improve performance.
Avoid frequent resizing: Adding elements frequently can cause resizing. Consider setting an appropriate initial capacity.
Use immutable keys: Using mutable objects as keys can lead to unpredictable behavior.

6. Performance Considerations

Logarithmic time performance: TreeMap provides logarithmic time performance for basic operations like put, get, and remove.
Memory usage: Each entry in a TreeMap requires additional memory for storing tree structure.
Thread safety: TreeMap is not synchronized. Use Collections.synchronizedSortedMap() if thread safety is needed.

7. Real-time Example with CRUD Operations

Managing a Student Directory:

Student.java:

public class Student {
    private String name;
    private int age;

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

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    @Override
    public String toString() {
        return "Student{name='" + name + "', age=" + age + "}";
    }
}

Main.java:

import java.util.TreeMap;

public class Main {
    public static void main(String[] args) {
        TreeMap<Integer, Student> studentDirectory = new TreeMap<>();

        // Create
        studentDirectory.put(1, new Student("Aarav", 20));
        studentDirectory.put(2, new Student("Vivaan", 22));
        studentDirectory.put(3, new Student("Diya", 21));

        // Read
        for (TreeMap.Entry<Integer, Student> entry : studentDirectory.entrySet()) {
            System.out.println("ID: " + entry.getKey() + ", Student: " + entry.getValue());
        }

        // Update
        studentDirectory.put(2, new Student("Vivaan", 23));
        System.out.println("After Update:");
        for (TreeMap.Entry<Integer, Student> entry : studentDirectory.entrySet()) {
            System.out.println("ID: " + entry.getKey() + ", Student: " + entry.getValue());
        }

        // Delete
        studentDirectory.remove(1);
        System.out.println("After Deletion:");
        for (TreeMap.Entry<Integer, Student> entry : studentDirectory.entrySet()) {
            System.out.println("ID: " + entry.getKey() + ", Student: " + entry.getValue());
        }
    }
}

Output:

ID: 1, Student: Student{name='Aarav', age=20}
ID: 2, Student: Student{name='Vivaan', age=22}
ID: 3, Student: Student{name='Diya', age=21}
After Update:
ID: 2, Student: Student{name='Vivaan', age=23}
ID: 3, Student: Student{name='Diya', age=21}
After Deletion:
ID: 2, Student: Student{name='Vivaan', age=23}
ID: 3, Student: Student{name='Diya', age=21}

8. Conclusion

The TreeMap class in Java is a powerful class for managing key-value pairs in a sorted order. By understanding its methods, use cases, and best practices, you can effectively utilize TreeMap in your Java applications. This tutorial covers the essential methods with examples and demonstrates a real-time example with CRUD operations.

Java TreeMap Methods Tutorial with Examples

Table of Contents

1. Introduction

2. Key Points

3. TreeMap Methods

3.1. put()

3.2. putAll()

3.3. get()

3.4. remove()

3.5. clear()

3.7. isEmpty()

3.8. containsKey()

3.9. containsValue()

3.10. keySet()

3.11. values()

3.12. entrySet()

3.13. firstKey()

3.14. lastKey()

3.15. lowerKey()

3.16. higherKey()

3.17. floorKey()

3.18. ceilingKey()

3.19. pollFirstEntry()

3.20. pollLastEntry()

3.21. forEach()

3.22. replace()

3.23. compute()

3.24. computeIfAbsent()

3.25. computeIfPresent()

3.26. merge()

4. Use Cases

5. Best Practices

6. Performance Considerations

7. Real-time Example with CRUD Operations

8. Conclusion

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