Java

JAVA.COMPARE.EMPTYSTR : Comparison to Empty String (Java)

要旨

A string is compared to the empty string instead of using isEmpty().

This checker identifies incorrect or inefficient comparisons through equals() or ==. In some cases, these comparisons are wrong: for instance, strings should be compared for equality through equals() rather than through ==. Classes can be safely compared through == instead. In other cases, these comparisons can be replaced by more efficient code.

プロパティ

クラス名 Comparison to Empty String (Java)
日本語クラス名 Comparison to Empty String (Java)
クラス分類 信頼性 (reliability)
ニーモニック JAVA.COMPARE.EMPTYSTR
カテゴリー
CWE CWE:597 Use of Wrong Operator in String Comparison
CERT-Java CERT-Java:EXP03-J Do not use the equality operators when comparing values of boxed primitives
対応言語 Java で利用可能です。
有効/無効設定 このワーニングクラスのチェックはデフォルトで有効になっています。チェックを無効にするにはプロジェクト設定ファイル （configuration file）に以下の WARNING_FILTER ルールを追加してください。 
WARNING_FILTER += discard class="Comparison to Empty String (Java)"

例 

// Main.java
public class Main {
  public static boolean verbose;
  private final static String[] arr = new String[] { "verbose" };

  public static void main(String[] args) {
    if (args.length > 0)
      assert !args[0].equals("");                // Comparison to Empty String (Java)    
                                                 // warning issued here. 

    if (args.length > 0 && args[0] == "verbose") // Should Use equals() Instead of == (Java)     
                                                 // warning issued here. 
      verbose = true;

    if (args.equals(arr))                        // equals on Array (Java)    
                                                 // warning issued here. 
      verbose = true;

    if (args.length > 0) {
      Main m = new Main();
      System.out.println(m.test(args[0]));
      System.out.println(m.weAreRedefined());
    }
  }

  private boolean test(Object o) {
    return o == this;                            /* == Always Fails (Java)     
                                                  * warning issued here (objects are of incompatible type:  
                                                  * a String and an instance of Main. 
                                                  */ 
  }

  public boolean weAreRedefined() {
    return !getClass().equals(Main.class);       // Should Use == Instead of equals() (Java)
                                                 // warning issued here. 
  }
}

Each of these warnings corresponds to incorrect or inefficient comparisons. The programmer should rewrite the code as follows.

// Main.java, after modification
public class Main {
  public static boolean verbose;
  private final static String[] arr = new String[] { "verbose" };

  public static void main(String[] args) {
    if (args.length > 0)
      assert !args[0].isEmpty();

    if (args.length > 0 && args[0].equals("verbose"))
      verbose = true;

    if (java.util.Arrays.equals(args, arr))
      verbose = true;

    if (args.length > 0) {
      Main m = new Main();
      //System.out.println(m.test(args[0]));
      System.out.println(m.weAreRedefined());
    }
  }

  public boolean weAreRedefined() {
    return getClass() != Main.class;
  }
}

解決法

Check if the equality is actually wrong or can be replaced by more optimized code.

関連のある設定ファイルパラメータ

設定ファイルの以下のパラメータがこのワーニングクラスのチェックに影響します。