Resource leak in is never closed

Question

Why does Eclipse give me the warming  Resource leak   in  is never closed  in the following code   public void readShapeData             Scanner in   new Scanner System in           System out println  Enter the width of the Rectangle              width   in nextDouble            System out println  Enter the height of the Rectangle              height   in nextDouble

User · Answer

Scanner sc   new Scanner System in      do stuff with sc  sc close     write at end of code

User · Answer

Because you don t close your Scanner  in close

User · Answer

private static Scanner in    I fixed it by declaring in as a private static Scanner class variable  Not sure why that fixed it but that is what eclipse recommended I do

User · Answer

The Scanner should be closed  It is a good practice to close Readers  Streams   and this kind of objects to free up resources and aovid memory leaks  and doing so in a finally block to make sure that they are closed up even if an exception occurs while handling those objects

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An InputStream which is typically connected to keyboard input of console programs  Scanner in  new Scanner System in     above line will invoke Constructor of Scanner class with argument System in  and will return a reference to newly constructed object   It is connected to a Input Stream that is connected to Keyboard  so now at run-time you can take user input to do required operation     Write piece of code    To remove the memory leak -   in close     write at end of code

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Okay  seriously  in many cases at least  this is actually a bug  It shows up in VS Code as well  and it s the linter noticing that you ve reached the end of the enclosing scope without closing the scanner object  but not recognizing that closing all open file descriptors is part of process termination  There s no resource leak because the resources are all cleaned up at termination  and the process goes away  leaving nowhere for the resource to be held

User · Answer

As others have said  you need to call  close  on IO classes   I ll add that this is an excellent spot to use the try - finally block with no catch  like this   public void readShapeData   throws IOException       Scanner in   new Scanner System in       try           System out println  Enter the width of the Rectangle              width   in nextDouble            System out println  Enter the height of the Rectangle              height   in nextDouble          finally           in close              This ensures that your Scanner is always closed  guaranteeing proper resource cleanup   Equivalently  in Java 7 or greater  you can use the  try-with-resources  syntax   try  Scanner in   new Scanner System in

User · Answer

Generally  instances of classes that deal with I O should be closed after you re finished with them  So at the end of your code you could add in close

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If you are using JDK7 or 8  you can use try-catch with resources This will automatically close the scanner   try   Scanner scanner   new Scanner System in             System out println  Enter the width of the Rectangle          width   scanner nextDouble        System out println  Enter the height of the Rectangle          height   scanner nextDouble        catch Exception ex          exception handling   do something  e g   print the error message      ex printStackTrace

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It is telling you that you need to close the Scanner you instantiated on System in with Scanner close    Normally every reader should be closed   Note that if you close System in  you won t be able to read from it again  You may also take a look at the Console class   public void readShapeData         Console console   System console        double width   Double parseDouble console readLine  Enter the width of the Rectangle           double height   Double parseDouble console readLine  Enter the height of the Rectangle

User · Answer

adding private static Scanner in  does not really fix the problem  it only clears out the warning  Making the scanner static means it remains open forever  or until the class get s unloaded  which nearly is  forever     The compiler gives you no warning any more  since you told him  keep it open forever   But that is not what you really wanted to  since you should close resources as soon as you don t need them any more   HTH  Manfred

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You need call in close    in a finally block to ensure it occurs   From the Eclipse documentation  here is why it flags this particular problem  emphasis mine       Classes implementing the interface java io Closeable  since JDK 1 5    and java lang AutoCloseable  since JDK 1 7  are considered to   represent external resources  which should be closed using method   close    when they are no longer needed       The Eclipse Java compiler is able to analyze whether code using such   types adheres to this policy                The compiler will flag  violations  with  Resource leak   stream  is never closed     Full explanation here

User · Answer

in close    scannerObject close       It will close Scanner and shut the warning

User · Answer

You should close your Scanner when you re done with it   in close

[java] Resource leak: 'in' is never closed

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