Hashtable Example in Java

Introduction

HashTable 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

A hash table is a data structure used to implement an associative array, a structure that can map keys to values. A hash table uses a hash function to compute an index into an array of buckets or slots, from which the desired value can be found.

Syntax

Hashtable variable_name = new Hashtable();

HashTable Example Program

import java.util.Hashtable;
class HashTableExample{
	public static void main(String[] args){
        Hashtable ht = new Hashtable();
        ht.put(1,"FIRST");
        ht.put(2,"SECOND");
        ht.put(3,"THIRD");
		ht.put(4,"THIRD");
        System.out.println("Hashtable is "+ht);
        System.out.println("Value of key 2: "+ht.get(2));
        System.out.println("Size of the Hashtable is  "+ht.size());
    }
}

Sample Output

Hashtable is {4=THIRD, 3=THIRD, 2=SECOND, 1=FIRST}
Value of key 2: SECOND
Size of the Hashtable is  4

When to use

Use this hashtable 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.Hashtable; imports a class used later in the program.

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

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

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

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

7. Compare your console output with the sample output for HashTable 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.