JAVA.COMPARE.EQ : Should Use equals() Instead of == (Java)

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CodeSonar^® 9.2p0

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JAVA.COMPARE.EQ : Should Use equals() Instead of == (Java)

Summary

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.

Properties

Example

// 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;
  }
}

Resolution

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

Relevant Configuration File Parameters

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