Shell Sort Example in Java

Introduction

Shell Sort is a classic Java console program that demonstrates the concept with complete source code and sample output. Sorting algorithms arrange data in order — bubble, selection, merge, quick and heap sort.

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

Shellsort, also known as Shell sort or Shell’s method, is an in-place comparison sort. It can be seen as either a generalization of sorting by exchange or sorting by insertion. The method starts by sorting pairs of elements far apart from each other, then progressively reducing the gap between elements to be compared.

Shell Sort Example Program

class ShellSort {
    public static void main(String args[]) {
        int[] arr = new int[] { 300, 200, 500, 400, 100 };
		System.out.println("Array before sorting is ");
		for(int i=0;i 0; inc /= 2){
		for (int i = inc; i < arr.length; i++){
			k = arr[i];
			for (j = i; j >= inc; j -= inc) {
				if (k < arr[j - inc]) {
					arr[j] = arr[j - inc];
				} else {
					break;
				}
			}
			arr[j] = k;
		}
	}
	System.out.println("After Sorting is ");
	for (int i = 0; i < 5; i++) {
		System.out.println(arr[i]);
	}
    }
}

Sample Output

Array before sorting is
300
200
500
400
100
After Sorting is
100
200
300
400
500

When to use

Use this shell sort 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. int[] arr = new int[] { 300, 200, 500, 400, 100 }; updates a variable used in the calculation or output.

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

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

5. for (int i = inc; i < arr.length; i++){ updates a variable used in the calculation or output.

6. k = arr[i]; updates a variable used in the calculation or output.

7. for (j = i; j >= inc; j -= inc) { updates a variable used in the calculation or output.

8. The if statement runs the nested code only when the condition is true.

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.