Guava——Object common methods

equals

When your object fields can be null, implementing Object.equals can be a pain, because you have to check separately for null. Using Objects.equal lets you perform equals checks in a null-sensitive way, without risking a NullPointerException.

Objects.equal("a", "a"); // returns true
Objects.equal(null, "a"); // returns false
Objects.equal("a", null); // returns false
Objects.equal(null, null); // returns true

Note: The newly introduced Objects class in JDK 7 provides the equivalent Objects.equalsmethod.

hashCode

Hashing all the fields of an Object should be simpler. Guava's Objects.hashCode(Object...)creates a sensible, order-sensitive hash for the specified sequence of fields. Use Objects.hashCode(field1, field2, ..., fieldn) instead of building the hash by hand.

Note: The newly introduced Objects class in JDK 7 provides the equivalentObjects.hash(Object...).

toString

A good toString method can be invaluable in debugging, but is a pain to write. Use MoreObjects.toStringHelper() to easily create a useful toString. Some simple examples include:

// Returns "ClassName{x=1}"
   MoreObjects.toStringHelper(this)
       .add("x", 1)
       .toString();

   // Returns "MyObject{x=1}"
   MoreObjects.toStringHelper("MyObject")
       .add("x", 1)
       .toString();

compare/compareTo

Implementing a Comparator, or implementing the Comparable interface directly, can be a pain. Consider:

class Person implements Comparable<Person> {
  private String lastName;
  private String firstName;
  private int zipCode;

// ugly codes ugly codes ugly codes!!!
  public int compareTo(Person other) {
    int cmp = lastName.compareTo(other.lastName);
    if (cmp != 0) {
      return cmp;
    }
    cmp = firstName.compareTo(other.firstName);
    if (cmp != 0) {
      return cmp;
    }
    return Integer.compare(zipCode, other.zipCode);
  }
}

This code is easily messed up, tricky to scan for bugs, and unpleasantly verbose. We should be able to do better.

For this purpose, Guava provides ComparisonChain.

ComparisonChain performs a "lazy" comparison:it only performs comparisons until it finds a nonzero result, after which it ignores further input.