CODEWITHSUNDEEP
javadatainputstream
Lesya Makhova
Lesya Makhova

Reputation: 1430

DataInputStream who close stream if IOException

In all examples everybody can find code like this:

DataInputStream inputStream = null;
try {
    inputStream = new DataInputStream( new FileInputStream("file.data"));
    int i = inputStream.readInt();
    inputStream.close();
} catch (FileNotFoundException e) { 
    //print message File not found
} catch (IOException e) { e.printStackTrace() }

When this code met FileNotFound exception, inputStream was not open, so it doesn't need to be closed.

But why when IOException mets in that catch block I don't see inputStream.close(). This operation did's automatically when input data exception throws? Because if programm has problem with input this means that stream already open.

Upvotes: 1

Views: 2190

Answers (3)

Andremoniy
Andremoniy

Reputation: 34920

No, close operation doesn't invoke automatically. For this purposes use try-with-resources introduced in Java 7:

try (DataInputStream inputStream = new DataInputStream( new FileInputStream("file.data"))) {
    int i = inputStream.readInt();
} catch (Exception e) { e.printStackTrace() }

UPD: Explanation: DataInputStream implements AutoCloseable interface. That means, that in construction try-with-resources Java automatically will call close() method of inputStream in hidden finally block.

Upvotes: 2

tam tam
tam tam

Reputation: 1900

Even if the file not found exception occurs the steam is open, you would simply need to close it again as well.

You should always add a finally block in your try catch and close the stream. Finally will always execute if there is an exception

 finally {
            if(reader != null){
                try {
                    reader.close();
                } catch (IOException e) {
                    //do something clever with the exception
                }
            }
            System.out.println("--- File End ---");
        }

Upvotes: 2

MrSmith42
MrSmith42

Reputation: 10161

DataInputStream inputStream = null;
try {
    inputStream = new DataInputStream( new FileInputStream("file.data"));
    int i = inputStream.readInt();
} catch (FileNotFoundException e) { 
  //print message File not found
} catch (IOException e) { 
  e.printStackTrace();
} finally{
  if(null!=inputStream)
    inputStream.close();
}

Upvotes: 2

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