Sort array with sorted collection construction.
public class WordList {
public static void main(String[] args) {
Set<String> s = new TreeSet<String>();
// This will sort and filter the duplicated items in the string array automatically.
Collections.addAll(s, args);
System.out.println(s);
}
}
The interface
public interface Comparable<T> {
int compareTo(T t);
}
public final class CaseInsensitiveString
implements Comparable<CaseInsensitiveString> {
public int compareTo(CaseInsensitiveString cis) {
return String.CASE_INSENSITIVE_ORDER.compare(s, cis.s);
}
... // Remainder omitted
}
Implementation Key point
• The implementor must ensure sgn(x.compareTo(y)) == -sgn(y.compareTo(x))for all x and y. (This implies that x.compareTo(y)must throw an exception if and only if y.compareTo(x)throws an exception.)
• The implementor must also ensure that the relation is transitive: (x.compareTo(y) > 0 && y.compareTo(z) > 0)implies x.compareTo(z) > 0.
• Finally, the implementor must ensure that x.compareTo(y) == 0 implies that
sgn(x.compareTo(z)) == sgn(y.compareTo(z)), for all z.
• It is strongly recommended, but not strictly required, that (x.compareTo(y)== 0) == (x.equals(y)). Generally speaking, any class that implements the Comparable interface and violates this condition should clearly indicate this fact. The recommended language is "Note: This class has a natural ordering
that is inconsistent with equals."
Note
Compare integral primitive fields using the relational operators < and >. For floating-point fields, use Double.compare or Float.compare in place of the relational operators, which do not obey the general contract for compareTo when applied to floating point values. For array fields, apply these guidelines to each element.
// Normal implementation
public int compareTo(PhoneNumber pn) {
// Compare area codes
if (areaCode < pn.areaCode)
return -1;
if (areaCode > pn.areaCode)
return 1;
// Area codes are equal, compare prefixes
if (prefix < pn.prefix)
return -1;
if (prefix > pn.prefix)
return 1;
// Area codes and prefixes are equal, compare line numbers
if (lineNumber < pn.lineNumber)
return -1;
if (lineNumber > pn.lineNumber)
return 1;
return 0; // All fields are equal
}
/* The code below should be used when you're certain the fields in question are non-negative or, more generally, that the difference between the lowest and highest possible field values is less than or equal to Integer.MAX_VALUE(231-1).
*/
public int compareTo(PhoneNumber pn) {
// Compare area codes
int areaCodeDiff = areaCode - pn.areaCode;
if (areaCodeDiff != 0)
return areaCodeDiff;
// Area codes are equal, compare prefixes
int prefixDiff = prefix - pn.prefix;
if (prefixDiff != 0)
return prefixDiff;
// Area codes and prefixes are equal, compare line numbers
return lineNumber - pn.lineNumber;
}