CodeBlanks Logo Icon CodeBlanks
Login Register

try/catch

Learn to catch exceptions with try/catch.

Catch errors with try/catch

An exception is an unexpected condition that disrupts the normal flow of a program. The try block wraps error-prone code; catch catches and handles the error.

try {
  int result = 10 / 0;
} catch (ArithmeticException e) {
  System.out.println("Sıfıra bölme");
}

When an exception is thrown, the try block is interrupted and the matching catch takes over. If it is not caught, the program crashes. The type in the catch parentheses determines which exception is caught. The e variable carries the exception details.

The catch parameter and type

The type in the catch parentheses determines which exceptions are caught. ArithmeticException catches only arithmetic errors; if another type comes, the catch does not engage.

catch (ArithmeticException e) {
  System.out.println(e.getMessage());
}

getMessage() returns a short description of the exception. The e variable name is free; you can write ex or err. Making the type general (e.g. Exception) catches more but loses detail, so it is better to pick as specific a type as possible.

Practice Catch division by zero

Divide int a = 10; int b = 0;. Wrap in try; catch ArithmeticException and print Sıfıra bölme.

Starter code

Main.java
public class Main {
  public static void main(String[] args) {
    int a = 10;
    int b = 0;
    // attempt the division, catch the error, print a message
  }
}

Sample solution

Main.java
try {
  int result = a / b;
  System.out.println(result);
} catch (ArithmeticException e) {
  System.out.println("Sıfıra bölme");
}

Expected output

Sıfıra bölme

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What happens when an exception is thrown in a try block?

  • The try block continues
  • The program crashes immediately
  • Nothing happens
  • The matching catch block takes over Correct answer

Explanation: when an exception is thrown, the try is interrupted and the catch with a matching type runs.

2 Complete the catch block

Question 
try {
  int r = 10 / 0;
} ____ (ArithmeticException e) {
  System.out.println("Hata");
}
Answer 
try {
  int r = 10 / 0;
} catch (ArithmeticException e) {
  System.out.println("Hata");
}

Explanation: the catch block comes after try and catches the exception.

3 Match each exception to its scenario

Term Meaning
ArithmeticException Division by zero
NullPointerException null object
ArrayIndexOutOfBoundsException Out of bounds index
NumberFormatException Invalid number

All lessons in Beginner

1 Java basics

  1. What is Java?
  2. The main method
  3. Comments
  4. Class skeleton
  5. javac and java
  6. Summary - Java basics

2 Variables

  1. int and double
  2. boolean
  3. String
  4. Naming variables
  5. final variables
  6. Summary - Variables

3 Data types

  1. Primitive types
  2. Type casting
  3. String concatenation
  4. Math class
  5. BigInteger and BigDecimal
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add/subtract
  3. Multiply/divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic
  2. Comparison
  3. Logical
  4. Bitwise
  5. Assignment and increment
  6. Summary - Operators

6 String basics

  1. length and charAt
  2. equals and equalsIgnoreCase
  3. indexOf and substring
  4. toUpperCase and trim
  5. String.format
  6. Summary - String basics

7 Conditionals

  1. The if statement
  2. else and else if
  3. Nested if
  4. switch
  5. Ternary
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. do-while
  4. break and continue
  5. for-each
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Updating quantity
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. Filling arrays
  4. Multi-dimensional arrays
  5. Copying arrays
  6. Summary - Arrays

11 Array methods

  1. Arrays.sort
  2. Arrays.toString
  3. Arrays.binarySearch
  4. Arrays.copyOf
  5. Arrays.fill
  6. Summary - Array methods

12 Collections

  1. ArrayList
  2. add and get
  3. HashMap
  4. put and get
  5. HashSet
  6. Summary - Collections

13 Methods

  1. Defining methods
  2. return
  3. void methods
  4. Method overloading
  5. Scope
  6. Summary - Methods

14 Method parameters

  1. Primitive parameters
  2. Object parameters
  3. varargs
  4. Multiple values via array
  5. final parameters
  6. Summary - Method parameters

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 String builder

  1. StringBuilder
  2. append
  3. insert and delete
  4. reverse
  5. toString
  6. Summary - String builder

17 Input and output

  1. Scanner
  2. nextInt and nextLine
  3. System.out.printf
  4. BufferedReader
  5. try-with-resources
  6. Summary - Input and output

18 Enum

  1. Declaring enums
  2. values and valueOf
  3. Enum fields
  4. Enum methods
  5. switch with enum
  6. Summary - Enum

19 Exception basics

  1. try/catch
  2. finally
  3. throw
  4. Exception hierarchy
  5. Multiple catch
  6. Summary - Exception basics

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together