JAVA.TYPE.ARRAYTOSTRING : toString on Array (Java)

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JAVA.TYPE.ARRAYTOSTRING : toString on Array (Java)

Summary

Arrays are instances of java.lang.Object in Java. As a consequence, all methods of java.lang.Object can be invoked on arrays, However, this is not always sensible. In particular, calls to toString() yield a string derived from the unique identifier of the object, which is likely to be useless for the programmer and not her intent when she called toString().

Properties

Example

public class CallsOnArray {
  private static A[] array;

  public static void main(String[] args) {
    array = new A[args.length];
    for (int pos = 0; pos < args.length; pos++)
      array[pos] = new A(args[pos]);

    foo(array);

    System.out.println(array); // "toString on Array (Java)" warning issued here
  }

  private static void foo(Object o) {
    String s = o.toString();   // "toString on Array (Java)" warning issued here
    System.out.println(s);
  }

  private static class A {
    private int f;

    private A(String s) {
      this.f = s.length();
    }

    @Override
    public String toString() {
      return String.valueOf(f);
    }
  }
}

In this example, the programmer could replace the call to System.out.println(array) with a loop:

Resolution

Replace the call with a call to java.util.Arrays.toString(array) or with an explicit iteration over the elements of the array.

Relevant Configuration File Parameters

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