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

Related Vulnerabilities

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

References

[[JLS 05]] Section 14.4.2, Scope of Local Variable Declarations
[[Bloch 01]] 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