1. Common Errors
and Solutions
CST200 – Week 1: Common Errors when Starting
to write and compile Java Code
Instructor: Andreea Molnar

2. Outline
• Disclaimer
• Names
• Brackets
• Semicolons

3. Disclaimer

4. These are common errors I have seen as a
teaching assistant, and are based solely on
my experience.

5. Everyone is different, therefore:
•
•
•
some of you will not make these mistakes
others will not make these mistakes after
seeing this presentation
For others it may be a good resource to
consult

6. Error Category

7. Names

8. Names (e.g. class names, variable names,
method names) are a single string!

9. Is the class
name Hello or
World?
public class Hello World {
}

10. public class Hello World {
}
After the first
string –Hello –
a bracket is
expected.

11. public class Hello World {
}

12. public class Hello World {
}

13. public class HelloWorld {
}
public class Hello {
}
public class World {
}

14. Keep in mind, it is not only class names,
variable names and method names have
to be composed of a single connected
string.

15. public class HelloWorld {
public static void main(String [] args) {
int Britteny Spears;
}
}

16. public class HelloWorld {
public static void main(String [] args) {
int Britteny Spears;
}
}
After the first string
–Brittney – a ; is
expected.

17. public class HelloWorld {
public static void main(String [] args) {
int Britteny Spears;
}
}

18. public class HelloWorld {
public static void main(String [] args) {
int BrittenySpears;
int Britteny;
int Spears;
}
}

19. public class HelloWorld {
public static void main(String [] args) {
//this is the best
int brittenySpears;
int britteny;
int spears;
}
}

20. Brackets

21. Every open bracket has to be closed in the
program!!!

22. As a rule of thumb check that every
bracket you open is closed somewhere in
the program: (), [], {}.

23. For the purpose of this class use curly
brackets –{}- at the beginning and the end
of a class and a method (more about
these in the next week).

24. Every open bracket has to be closed in the
program!!!

25. public class HelloWorld {
public static void main(String [] args) {
System.out.println(“Hello World”);
}
}

26. public class HelloWorld {
//beginning of the class body
public static void main(String [] args) {
System.out.println(“Hello World”);
}
} //end of the class body

27. public class HelloWorld {
public static void main(String [] args) {
//beginning of the method body
System.out.println(“Hello World”);
} //end of the method body
}

28. Bracket
missing
public class HelloWorld
public static void main(String [] args) {
System.out.println(“Hello World”);
}
}
Bracket expected

29. Enjoy finding the other errors.

30. Semicolons

31. You have to learn to love ; in Java. Every
statement in Java ends with a ;.

32. public class HelloWorld {
public static void main(String [] args) {
System.out.println(“Hello World”);
}
}

33. Summary
• Names are a single string.
• Brackets always come in pairs.
• Semicolons end a statement.

34. Thank you