Page History

Arrays do not override the In Java, arrays are objects and support object methods such as Object.equals() method; the implementation of the . However, arrays do not support any methods besides those provided by Object. Consequently, using Object.equals() method on any array compares only array references rather than , not their contents. Programmers who wish to compare the contents of two arrays must use the twothe static two-argument Arrays.equals() method.   Two arrays are considered equal This method considers two arrays equivalent if both arrays contain the same number of elements, and all corresponding pairs of elements in the two arrays are equal.  equivalent, according to Object.equals(). In other words, two arrays are equal if they contain the same equivalent elements in the same order.  To  To test for reference equality, programmers can use the reference equality operators, == and !=.  

  Because the effect of using Object.equals() to compare two arrays is often misunderstoodmisconstrued as content equality, and because a better alternative exists in the use of reference equality operators, the use of the Object.equals() method to compare two arrays is disallowed by this rule.

Noncompliant Code Example

This noncompliant code example incorrectly uses the Object.equals() method to compare two arrays.:

public void arraysEqual() {
  int[] arr1 = new int[20]; // initializedInitialized to 0
  int[] arr2 = new int[20]; // initializedInitialized to 0
  System.out.println(arr1.equals(arr2)); // Prints false
}

Compliant Solution

This compliant solution compares the content of two arrays using the two-argument Arrays.equals() method.:

public void arrayContentsEqual() {
  int[] arr1 = new int[20]; // initializedInitialized to 0
  int[] arr2 = new int[20]; // initializedInitialized to 0
  System.out.println(Arrays.equals(arr1, arr2)); // Prints true
}

Compliant Solution

This compliant solution compares the array references using the reference equality operators ==.:

public void arrayReferencesEqual(int[] arr1 = new int[20] arr1, ; // Initialized to 0
int[] arr2) {
  arr1  = new int[20]; // Initialized to 0
System.out.println(arr1 == arr2); // Prints false 
}

Risk Assessment

Using the equals() method or relational operators with the intention of comparing array contents produces incorrect results, which can lead to vulnerabilities.

Automated Detection

Static detection of calls to to Object.equals() is straightforward. However, it is not always possible to statically resolve the class of a method invocation's target. Consequently, it may not always be possible to determine when Object.equals() is invoked for an array type.

Related Guidelines

Bibliography

...

[Seacord 2015]

Image Added EXP02-J. Do not use the Object.equals () method to compare two arrays LiveLesson

...

Image Added Image Added Image Added Never dereference null pointers      02. Expressions (EXP)      Image Removed