Scope minimization helps to capture 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 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 rather obtuse outcome.

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 scope 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 for only one operation if possible. This simplicity avoids variables from existing in overlapping scopes and prevents errors.

Risk Assessment

Using a larger scope than 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

\[[JLS 05|AA. Java References#JLS 05]\] [Section 14.4.2, Scope of Local Variable Declarations|http://java.sun.com/docs/books/jls/third_edition/html/statements.html#14.4.2]
\[[Bloch 01|AA. Java References#Bloch 01]\] Item 29, Minimize the scope of local variables

04. Scope (SCP)      04. Scope (SCP)      SCP01-J. Declare sensitive methods private or final, fields private and final, and classes to be final