This content originally appeared on DEV Community and was authored by Vigneshwaralingam
Common Java Errors in a Hello World Program and How to Fix Them
In this blog, we will:
Introduce a basic Hello World program in Java.
Identify 15 common errors that beginners make.
Explain why these errors happen and how to fix them.
Correct Hello World Program in Java
Before we explore errors, let’s look at a correct Hello World program:
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
This program will print:
Hello, World!
Now, let’s introduce 15 common errors and their fixes.
15 Common Errors in Java and Their Solutions
1⃣ Error: Misspelled main
method
Wrong Code:
public class HelloWorld {
public static void Main(String[] args) { // ❌ "Main" should be "main"
System.out.println("Hello, World!");
}
}
Fix:
public class HelloWorld {
public static void main(String[] args) { // ✅ Use lowercase "main"
System.out.println("Hello, World!");
}
}
Why? Java is case-sensitive. The JVM looks for
main
, not Main
.
2⃣ Error: Missing Semicolon (;
)
Wrong Code:
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!") // ❌ Missing semicolon
}
}
Fix:
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!"); // ✅ Add semicolon
}
}
Why? Java statements must end with a semicolon.
3⃣ Error: Incorrect System.out.println
Syntax
Wrong Code:
public class HelloWorld {
public static void main(String[] args) {
System.Out.Println("Hello, World!"); // ❌ "Out" and "Println" are incorrect
}
}
Fix:
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!"); // ✅ Use "out" and "println" (lowercase)
}
}
Why?
System.out.println
must be lowercase (out
and println
).
4⃣ Error: Missing Curly Braces ({}
)
Wrong Code:
public class HelloWorld
public static void main(String[] args) { // ❌ Missing opening brace `{`
System.out.println("Hello, World!");
}
Fix:
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
Why? Every class and method must have
{}
to define their scope.
5⃣ Error: Class Name and Filename Mismatch
Wrong Code: (File is saved as
Hello.java
)
public class HelloWorld { // ❌ Class name "HelloWorld" does not match filename "Hello.java"
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
Fix:
- Either rename the file to HelloWorld.java, or
- Change the class name to Hello
Why? The filename must match the class name when using
public class
.
6⃣ Error: Using void
in the Wrong Place
Wrong Code:
public class HelloWorld {
public void static main(String[] args) { // ❌ "void" should not be here
System.out.println("Hello, World!");
}
}
Fix:
public class HelloWorld {
public static void main(String[] args) { // ✅ "void" should not be before "static"
System.out.println("Hello, World!");
}
}
Why?
static
comes before void
in the main method declaration.
7⃣ Error: Missing public
Keyword for the Class
Wrong Code:
class HelloWorld { // ❌ Missing "public"
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
Fix:
public class HelloWorld { // ✅ Add "public"
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
Why? Java expects the main class to be
public
if it’s the main entry point.
8⃣ Error: Using Single Quotes Instead of Double Quotes
Wrong Code:
public class HelloWorld {
public static void main(String[] args) {
System.out.println('Hello, World!'); // ❌ Uses single quotes
}
}
Fix:
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!"); // ✅ Use double quotes
}
}
Why? Strings in Java must be enclosed in double quotes (
""
), not single quotes (''
).
9⃣ Error: Using println
without System.out
Wrong Code:
public class HelloWorld {
public static void main(String[] args) {
println("Hello, World!"); // ❌ "println" needs "System.out"
}
}
Fix:
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!"); // ✅ Use "System.out.println"
}
}
Why?
println
is a method of System.out
, so it must be used with System.out
.
Summary of Common Errors
Error Type | Mistake | Fix |
---|---|---|
Syntax Error | Misspelled main
|
Use main , not Main
|
Syntax Error | Missing semicolon | Add ; at the end |
Syntax Error | Wrong System.out.println
|
Use lowercase out.println
|
Compilation Error | Class and filename mismatch | Rename the file or class |
Compilation Error | Missing public keyword |
Add public before class
|
Logical Error | Wrong string quotes | Use "" instead of ''
|
Final Thoughts
Errors are a part of learning Java programming. The key to mastering coding is:
Reading error messages carefully
Practicing regularly
Using an IDE (like IntelliJ or VS Code) for auto-suggestions
Debugging step by step
What was the most frustrating error you faced in Java? Let me know in the comments!
This content originally appeared on DEV Community and was authored by Vigneshwaralingam