Java

JAVA.COMPARE.EQARRAY : equals on Array (Java)

Summary

Two arrays are compared with equals().

This checks whether or not they are exactly the same object. If the intent is to check whether they have the same contents, perform element-wise comparison instead.

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

Class Name equals on Array (Java)
Significance reliability
Mnemonic JAVA.COMPARE.EQARRAY
Categories
CWE CWE:595 Comparison of Object References Instead of Object Contents
CERT-Java CERT-Java:EXP02-J Do not use the Object.equals() method to compare two arrays
  CERT-Java:EXP03-J Do not use the equality operators when comparing values of boxed primitives
Availability Available for Java only.
Enabling Checks for this warning class are enabled by default. To disable them, add the following WARNING_FILTER rule to the project configuration file. 
WARNING_FILTER += discard class="equals on Array (Java)"

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.