SCP00-J. Use as minimal scope as possible for all variables

Scope minimization helps in capturing common programming errors, improves code readability by tying together the declaration and actual use of a variable and eases maintainability because unused variables are easily caught and removed.

Noncompliant Code Example

This noncompliant code example shows a variable that is declared outside the for loop. This can harm reusability as the loop index i will change after the for statement. Consider for instance, the case when this code snippet is copy pasted with the intent of using a different index j but the statement mistakenly still iterates over index i. As i is still in scope, this will lead to a unexpected behavior.

public class Scope {
  public static void main(String[] args) {
    int i = 0;
    for(i = 0; i < 10; i++) {
      // Do operations
    }
  }
}

Compliant Solution

To be compliant, minimize the scope of variables where possible, such as by declaring loop indexes within the for statement.

public class Scope {
  public static void main(String[] args) {
    for(int i = 0; i < 10; i++) { //contains declaration
      // Do operations
    }
  }
}

Additionally, methods should be designed to perform only one operation if possible. This reduces the need for variables existing in overlapping scopes and consequently, helps prevent errors.

Risk Assessment

Using a larger scope than what is necessary results in less reliable code.

Automated Detection

TODO

Other Languages

This rule appears in the C Secure Coding Standard as DCL19-C. Use as minimal a scope as possible for all variables and functions.

This rule appears in the C++ Secure Coding Standard as DCL07-CPP. Use as minimal scope as possible for all variables and methods.

Related Vulnerabilities

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

Bibliography

[[JLS 2005]] Section 14.4.2, Scope of Local Variable Declarations
[[Bloch 2001]] Item 29, Minimize the scope of local variables

05. Scope (SCP)      05. Scope (SCP)      SCP01-J. Do not increase the accessibility of overridden or hidden methods