Implementing the Comparable interface in Java give the object a natural ordering, as in makes it Sortable. The comparable interface only has one method:
public interface Comparable {
int compareTo(T t);
}CompareTo only requires a output of negative integer, zero or positive integer representing less than, equals to, or greater than. Also be aware that if object returns a compareTo value of 0 (Equals to) it is not the same as calling equals on the object. For example new BigDecimal(“5.0”) and new BigDecimal(“5.00”) returns false on equals but 0 on compareTo!
When comparing multiple fields it is important to remember the order you compare them, start with the most significant fields! Below is a example of how to implement compareTo:
public class TestClass implements Comparable<TestClass> {
int id;
int value01;
int Date value02;
// Left out constructor, getters, hashCode, equals
@Override
public int compareTo(TestClass o) {
if (this == o)
return 0;
int diff = id - o.id;
if (diff != 0)
return diff;
diff = value01 - 0.value01;
if (diff != 0)
return diff;
if (value02 == null) {
if (o.value02 == null) {
return 0
}
return -1;
}
if (0.value02 == null) {
return 1;
}
return value02.compareTo(o.value02);
}
}