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Methods can return values to signify communicate failure or success or , at other times, to update the caller's local objects or fields. Security risks can arise if when method return values are simply ignored or if suitable action is not taken on their receiptwhen the invoking method fails to take suitable action. Consequently, programs must not ignore method return values.

When getter methods are named after an action, a programmer could fail to realize that a return value is expected. For example, the only purpose of the ProcessBuilder.redirectErrorStream() method is to report via return value whether the process builder successfully merged standard error and standard output. The method that actually performs redirection of the error stream is the overloaded single-argument method ProcessBuilder.redirectErrorStream(boolean).

Noncompliant Code Example (File Deletion)

This noncompliant code example attempt attempts to delete a file , but does not fails to check that whether the operation succeeds.has succeeded:

public void deleteFile(){

  File someFile = new File("someFileName.txt");

  // doDo something with someFile

  someFile.delete();

}

Compliant Solution

In the This compliant solution , checks the (boolean) Boolean value returned by the delete() method is checked and, if necessary, the error is handled.and handles any resulting errors:

public void deleteFile(){

  File someFile = new File("someFileName.txt");

  // doDo something with someFile

  if (!someFile.delete()) {
    // handleHandle thefailure factto thatdelete the file
 has not been deleted
   }

}

Noncompliant Code Example (String Replacement)

This noncompliant code example ignores the return value while making use of the String.replace() method. As a result, the original string is not updated even though it seems otherwise, 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 IgnoreReplace {
  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. 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.

Compliant Solution

The This compliant solution correctly updates the original string object by assigning to it String reference original with the return value from the String.replace() method:

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

Yet another source of coding bugs caused by ignoring return values is detailed in FIO03-J. Keep track of bytes read and account for character encoding while reading data.

Risk Assessment

Ignoring method return values may can lead to erroneous computation which, in turn, may lead to security risksunexpected program behavior.

Automated Detection

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TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Other Languages

Tool	Version	Checker	Description
CodeSonar	Include Page CodeSonar_V CodeSonar_V	JAVA.NULL.RET.UNCHECKED JAVA.FUNCS.IRV	Call Might Return Null (Java) Ignored Return Value (Java)
Coverity	7.5	CHECKED_RETURN	Implemented
Parasoft Jtest	Include Page Parasoft_V Parasoft_V	CERT.EXP00.NASSIG CERT.EXP00.AECB	Ensure method and constructor return values are used Avoid "try", "catch" and "finally" blocks with empty bodies
PVS-Studio	Include Page PVS-Studio_V PVS-Studio_V	V6010, V6101
SonarQube	Include Page SonarQube_V SonarQube_V	S2201 S899	Return values from functions without side effects should not be ignored Return values should not be ignored when they contain the operation status code
SpotBugs	Include Page SpotBugs_V SpotBugs_V	RV_RETURN_VALUE_IGNORED RV_RETURN_VALUE_IGNORED_INFERRED RV_RETURN_VALUE_IGNORED_NO_SIDE_EFFECT RV_RETURN_VALUE_IGNORED_BAD_PRACTICE RV_RETURN_VALUE_OF_PUTIFABSENT_IGNORED RR_NOT_CHECKED SR_NOT_CHECKED	Implemented

Related Guidelines

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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

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Image Added Image Added Image Added

References

\[[API 06|AA. Java References#API 06]\] method [delete()|http://java.sun.com/javase/6/docs/api/java/io/File.html#delete()]
\[[API 06|AA. Java References#API 06]\] method [replace()|http://java.sun.com/javase/6/docs/api/java/lang/String.html#replace(char,%20char)]
\[[Green 08|AA. Java References#Green 08]\] ["String.replace"|http://mindprod.com/jgloss/gotchas.html]
\[[MITRE 09|AA. Java References#MITRE 09]\] [CWE ID 252|http://cwe.mitre.org/data/definitions/252.html] "Unchecked Return Value"

EXP00-J. Use the same type for the second and third operands in conditional expressions      02. Expressions (EXP)      EXP03-J. Do not compare string objects using equality or relational operators