What is the importance of try and catch block?

The

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

5 block in Java is used to handle exceptions and prevents the abnormal termination of the program.

Here's the syntax of a

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

5 block in Java.

try{
  // code
}
catch(exception) {
  // code
}

The

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

7 block includes the code that might generate an exception.

The

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

8 block includes the code that is executed when there occurs an exception inside the

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

7 block.

Example: Java try...catch block

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

Output

ArithmeticException => / by zero

In the above example, notice the line,

int divideByZero = 5 / 0;

Here, we are trying to divide a number by zero. In this case, an exception occurs. Hence, we have enclosed this code inside the

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

7 block.

When the program encounters this code,

ArithmeticException => / by zero

1 occurs. And, the exception is caught by the

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

8 block and executes the code inside the

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

8 block.

The

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

8 block is only executed if there exists an exception inside the

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

7 block.

Note: In Java, we can use a

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

7 block without a

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

8 block. However, we cannot use a

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

8 block without a

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

7 block.

---

Java try...finally block

We can also use the

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

7 block along with a finally block.

In this case, the finally block is always executed whether there is an exception inside the try block or not.

Example: Java try...finally block

class Main {
  public static void main(String[] args) {
    try {
      int divideByZero = 5 / 0;
    }

    finally {
      System.out.println("Finally block is always executed");
    }
  }
}

Output

Finally block is always executed
Exception in thread "main" java.lang.ArithmeticException: / by zero
        at Main.main(Main.java:4)

In the above example, we have used the

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

7 block along with the

int divideByZero = 5 / 0;

2 block. We can see that the code inside the

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

7 block is causing an exception.

However, the code inside the

int divideByZero = 5 / 0;

2 block is executed irrespective of the exception.

---

In Java, we can also use the finally block after the

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

5 block. For example,

import java.io.*;

class ListOfNumbers {

  // create an integer array
  private int[] list = {5, 6, 8, 9, 2};

  // method to write data from array to a fila
  public void writeList() {
    PrintWriter out = null;

    try {
      System.out.println("Entering try statement");

      // creating a new file OutputFile.txt
      out = new PrintWriter(new FileWriter("OutputFile.txt"));

      // writing values from list array to Output.txt
      for (int i = 0; i < 7; i++) {
        out.println("Value at: " + i + " = " + list[i]);
      }
    }
    
    catch (Exception e) {
      System.out.println("Exception => " + e.getMessage());
    }
    
    finally {
      // checking if PrintWriter has been opened
      if (out != null) {
        System.out.println("Closing PrintWriter");
        // close PrintWriter
        out.close();
      }
      
      else {
        System.out.println("PrintWriter not open");
      }
    }

  }
}

class Main {
  public static void main(String[] args) {
    ListOfNumbers list = new ListOfNumbers();
    list.writeList();
  }
}

Output

Entering try statement
Exception => Index 5 out of bounds for length 5
Closing PrintWriter

In the above example, we have created an array named list and a file named output.txt. Here, we are trying to read data from the array and storing to the file.

Notice the code,

for (int i = 0; i < 7; i++) {
  out.println("Value at: " + i + " = " + list[i]);
}

Here, the size of the array is

int divideByZero = 5 / 0;

6 and the last element of the array is at

int divideByZero = 5 / 0;

7. However, we are trying to access elements at

int divideByZero = 5 / 0;

8 and

int divideByZero = 5 / 0;

9.

Hence, the code generates an exception that is caught by the catch block.

Since the

int divideByZero = 5 / 0;

2 block is always executed, we have included code to close the

class Main {
  public static void main(String[] args) {
    try {
      int divideByZero = 5 / 0;
    }

    finally {
      System.out.println("Finally block is always executed");
    }
  }
}

1 inside the finally block.

It is a good practice to use finally block to include important cleanup code like closing a file or connection.

Note: There are some cases when a

int divideByZero = 5 / 0;

2 block does not execute:

• Use of

  class Main {
    public static void main(String[] args) {
      try {
        int divideByZero = 5 / 0;
      }
  
      finally {
        System.out.println("Finally block is always executed");
      }
    }
  }

  3 method
• An exception occurs in the

  int divideByZero = 5 / 0;

  2 block
• The death of a thread

---

For each

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

7 block, there can be zero or more

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

8 blocks. Multiple

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

8 blocks allow us to handle each exception differently.

The argument type of each

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

8 block indicates the type of exception that can be handled by it. For example,

class ListOfNumbers {
  public int[] arr = new int[10];

  public void writeList() {

    try {
      arr[10] = 11;
    }
    
    catch (NumberFormatException e1) {
      System.out.println("NumberFormatException => " + e1.getMessage());
    }
    
    catch (IndexOutOfBoundsException e2) {
      System.out.println("IndexOutOfBoundsException => " + e2.getMessage());
    }

  }
}

class Main {
  public static void main(String[] args) {
    ListOfNumbers list = new ListOfNumbers();
    list.writeList();
  }
}

Output

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

0

In this example, we have created an integer array named

class Main {
  public static void main(String[] args) {
    try {
      int divideByZero = 5 / 0;
    }

    finally {
      System.out.println("Finally block is always executed");
    }
  }
}

9 of size 10.

Since the array index starts from 0, the last element of the array is at

Finally block is always executed
Exception in thread "main" java.lang.ArithmeticException: / by zero
        at Main.main(Main.java:4)

0. Notice the statement,

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

1

Here, we are trying to assign a value to the index 10. Hence,

Finally block is always executed
Exception in thread "main" java.lang.ArithmeticException: / by zero
        at Main.main(Main.java:4)

1 occurs.

When an exception occurs in the

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

7 block,

• The exception is thrown to the first

  class Main {
    public static void main(String[] args) {
  
      try {
        int divideByZero = 5 / 0;
        System.out.println("Rest of code in try block");
      }
  
      catch (ArithmeticException e) {
        System.out.println("ArithmeticException => " + e.getMessage());
      }
    }
  }

  8 block. The first

  class Main {
    public static void main(String[] args) {
  
      try {
        int divideByZero = 5 / 0;
        System.out.println("Rest of code in try block");
      }
  
      catch (ArithmeticException e) {
        System.out.println("ArithmeticException => " + e.getMessage());
      }
    }
  }

  8 block does not handle an

  Finally block is always executed
  Exception in thread "main" java.lang.ArithmeticException: / by zero
          at Main.main(Main.java:4)

  5, so it is passed to the next

  class Main {
    public static void main(String[] args) {
  
      try {
        int divideByZero = 5 / 0;
        System.out.println("Rest of code in try block");
      }
  
      catch (ArithmeticException e) {
        System.out.println("ArithmeticException => " + e.getMessage());
      }
    }
  }

  8 block.
• The second

  class Main {
    public static void main(String[] args) {
  
      try {
        int divideByZero = 5 / 0;
        System.out.println("Rest of code in try block");
      }
  
      catch (ArithmeticException e) {
        System.out.println("ArithmeticException => " + e.getMessage());
      }
    }
  }

  8 block in the above example is the appropriate exception handler because it handles an

  Finally block is always executed
  Exception in thread "main" java.lang.ArithmeticException: / by zero
          at Main.main(Main.java:4)

  5. Hence, it is executed.

---

Catching Multiple Exceptions

From Java SE 7 and later, we can now catch more than one type of exception with one

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

8 block.

This reduces code duplication and increases code simplicity and efficiency.

Each exception type that can be handled by the

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

8 block is separated using a vertical bar

import java.io.*;

class ListOfNumbers {

  // create an integer array
  private int[] list = {5, 6, 8, 9, 2};

  // method to write data from array to a fila
  public void writeList() {
    PrintWriter out = null;

    try {
      System.out.println("Entering try statement");

      // creating a new file OutputFile.txt
      out = new PrintWriter(new FileWriter("OutputFile.txt"));

      // writing values from list array to Output.txt
      for (int i = 0; i < 7; i++) {
        out.println("Value at: " + i + " = " + list[i]);
      }
    }
    
    catch (Exception e) {
      System.out.println("Exception => " + e.getMessage());
    }
    
    finally {
      // checking if PrintWriter has been opened
      if (out != null) {
        System.out.println("Closing PrintWriter");
        // close PrintWriter
        out.close();
      }
      
      else {
        System.out.println("PrintWriter not open");
      }
    }

  }
}

class Main {
  public static void main(String[] args) {
    ListOfNumbers list = new ListOfNumbers();
    list.writeList();
  }
}

1.

Its syntax is:

class Main {
  public static void main(String[] args) {

    try {
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }

    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

2

To learn more, visit Java catching multiple exceptions.

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Java try-with-resources statement

The try-with-resources statement is also referred to as automatic resource management. This statement automatically closes all the resources at the end of the statement.

What is the purpose of try and catch block?

Is try catch block necessary?