Treemap Example in Java

Introduction

TreeMap is a classic Java console program that demonstrates the concept with complete source code and sample output. The Collections Framework provides ArrayList, HashMap, HashSet and related data structures.

This tutorial walks through the program line by line, explains how the logic works, and highlights best practices you can apply in your own code.

Definition

Maps are defined by the java.util.Map interface in Java. Maps are simple data structures that associate a key with a value. The element is the value. This lets the map be very flexible. If the key is the hash code of the element, the map is essentially a set. If it’s just an increasing number, it becomes a list. Methods can be called that find the key or map entry that’s closest to the given key in either direction. The map can also be reversed, and an iterator in reverse order can be generated from it. It’s implemented by java.util.TreeMap.

Syntax

TreeMap marks = new TreeMap();

TreeMap Example Program

import java.util.TreeMap;
 
public class TreeMapDemo {
    public static void main(String[] args) {
        TreeMap marks = new TreeMap();
        marks.put("Student1", 120);
        marks.put("Student2", 190);
        marks.put("Student3", 89);
        marks.put("Student4", 142);
        for(String key: marks.keySet()){
			System.out.println(key  +" : "+ marks.get(key));
        }
    }
}

Sample Output

Student1 : 120
Student2 : 190
Student3 : 89
Student4 : 142

When to use

Use this treemap example when learning or revising core Java syntax.

How it works

1. Execution begins in the main method — the JVM calls this method when you run the class.

2. import java.util.TreeMap; imports a class used later in the program.

3. TreeMap marks = new TreeMap(); updates a variable used in the calculation or output.

4. A loop repeats the block until its condition becomes false.

5. A println / print call writes text to the console — part of the sample output below.

6. Compare your console output with the sample output for TreeMap to confirm the program behaves correctly.

Best Practices

• Use meaningful variable and class names that describe their purpose.
• Compile and run the program locally — modify values to see how output changes.
• Read compiler errors carefully; they usually point to the exact line to fix.

Common Mistakes

• Copying code without understanding each line — practice by changing one statement at a time.
• Mismatching the public class name and the .java filename.
• Forgetting semicolons at the end of statements.