Tips for Implementing Comparable

Comparable has a contract similar to equals’s.

• Comparable.compareTo() == 0 should usually be consistent with equals, but if it is not, you should explicit comment about this.
• Like equals, it is not always possible to obey both the contract and object-oriented principles while extending a class. Use composition instead.
• Be very careful about (signed) integer overflow when you implement Comparable. The difference between a positive 32-bit signed integer and a negative one could be greater than what a 32-bit signed integer can hold. (And this bug is very hard to locate.)

public int compareTo(Blob b) {
  // Danger: This might overflow!
  return intValue - b.intValue;
}