Runtime & Compile-time Errors

This note is (obviously) generated by ChatGPT, but it’s a neat overview of the types of errors that could occur in Java.

🧱 Compile-Time Errors (Detected during compilation)

🧠 Think: “Syntax and type rules broken” — Java can’t even build the program.

🔹 Types

1. Syntax Errors

   • Missing semicolons

   • Unmatched brackets/braces/parentheses

   • Incorrect use of Java keywords

2. Type Errors

   • Incompatible types (e.g., assigning a double to an int without a cast)

   • Calling a method with the wrong parameter types

   • Using undeclared variables

3. Missing Class or Method Definitions

   • Trying to instantiate an undefined class

   • Calling a non-existent method

4. Access Errors

   • Trying to access private members from outside the class

   • Using incorrect static vs. non-static context

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💥 Runtime Errors (Occur while the program is running)

🧠 Think: “Program builds but crashes during execution”

🔸 Types

1. NullPointerException

   • Accessing a method or field of a null reference

2. ArithmeticException

   • Division by zero

3. ArrayIndexOutOfBoundsException

   • Accessing an array index that doesn’t exist

4. ClassCastException

   • Improper casting between unrelated types

5. IllegalArgumentException

   • Passing invalid arguments to methods (common in math/util libraries)

6. StringIndexOutOfBoundsException

   • Accessing invalid index of a string (e.g., charAt(-1) or charAt(length))