JAVA.STRUCT.EXCP.EEH : Empty Exception Handler (Java)

Summary

An exception handler has an empty body.

This checker controls if exception handlers might be incorrect. For instance, an exception handler with an empty body might be an unfinished snippet of code; an exception handler for a very generic exception type might end up catching too many exceptions, also some that were not meant to be caught there.

Properties

WARNING_FILTER += discard class="Empty Exception Handler (Java)"

Example

// Main.java 
import java.io.FileWriter;

public class Main {
  public static void main(String args[]) {
    FileWriter fw = null;
    try {
      fw = new FileWriter(args[0]);
      fw.close();
    }
    catch (IndexOutOfBoundsException e) {} // Empty Exception Handler (Java) warning issued here
    catch (Exception e) {                  // Generic Exception Handler (Java) warning issued here
      System.out.println("unusual");
    }
  }
}

These issues can be resolved as follows.

• Add content to the first exception handler so that it is not empty. For example, it could output a warning message to the user specifying that the program must be invoked with an argument
• Narrow the exception type caught by the second exception handler to java.io.IOException.

// Main.java, after modification 
import java.io.FileWriter;

public class Main {
  public static void main(String args[]) {
    FileWriter fw = null;
    try {
      fw = new FileWriter(args[0]);
      fw.close();
    }
    catch (IndexOutOfBoundsException e) {
      System.out.println("usage: Main filename");
    }
    catch (IOException e) {
      System.out.println("I/O error");
    }
  }
}

Resolution

Add a body to the exception handler, or narrow to the exception types.

Note

Sometimes, an empty handler is needed since the compiler does not know that an exception will never be thrown there. If the analyzer recognizes that situation, it will not issue any warning for the empty exception handler. For instance, in the following program:

public class CloneOK implements Cloneable {
  private int f;

  public CloneOK(int f) {
    this.f = f;
  }

  @Override
  protected Object clone() {
    CloneOK result = null;

    try {
      System.out.println("Starting cloning");
      result = (CloneOK) super.clone();
      result.f = f;
      System.out.println("Finished cloning");
    }
    catch (CloneNotSupportedException e) {
    }

    return result;
  }

  public static void main(String[] args) {
    new CloneOK(13).clone();
  }
}

This checker will not issue any warning, since the call to super.clone() is applied to a cloneable object this and will consequently never throw a CloneNotSupportedException. The programmer must nevertheless write that empty handler, since otherwise the compiler will not compile the program.

Relevant Configuration File Parameters

The following configuration file parameters affect checks for this warning class.

• REPORT_SIMILAR_WARNINGS
• WARNING_FILTER