Page History

...

This noncompliant code example attempts to delete a file but fails to check whether the operation has succeeded.:

public void deleteFile(){

  File someFile = new File("someFileName.txt");
  // doDo something with someFile
  someFile.delete();

}

...

This compliant solution checks the boolean Boolean value returned by the delete() method and handles any resulting errors.:

public void deleteFile(){

  File someFile = new File("someFileName.txt");
  // doDo something with someFile
  if (!someFile.delete()) {
    // handleHandle failure to delete the file
  }

}

...

This noncompliant code example ignores the return value of the String.replace() method, failing to update the original string. The String.replace() method cannot modify the state of the String (because String objects are immutable); rather, it returns a reference to a new String object containing the modified string.

public class Replace {
  public static void main(String[] args) {
    String original = "insecure";
    original.replace('i', '9');
    System.out.println(original);
  }
}

It is especially important to process the return values of immutable object methods. While Although many methods of mutable objects operate by changing some internal state of the object, methods of immutable objects cannot change the object and often return a mutated new object, leaving the original object unchanged.

...

This compliant solution correctly updates the String reference original with the return value from the String.replace() method.:

public class Replace {
  public static void main(String[] args) {
    String original = "insecure";
    original = original.replace('i', '9');
    System.out.println(original);
  }
}

...

Ignoring method return values can lead to unexpected program behavior.

Automated Detection

Related Guidelines

Bibliography

[API 2006]

method delete()

 

method replace()
[Green 2008]	String.replace
[Pugh 2009]	Misusing putIfAbsent
[Seacord 2015]	Image Added EXP00-J. Do not ignore values returned by methods LiveLesson

...

Image Added Image Added Image Added02. Expressions (EXP)      02. Expressions (EXP)      EXP01-J. Never dereference null pointers