SE450: Taxonomy: Immutable Data Classes [55/63]

We already have seen a basic version: Person.

Here is a more robust example:

file:Main.java [source] [doc-public] [doc-private]

01 02 03 04 05 06 07 08 package basics.immutabledata; public class Main { private Main() {} static public void main (final String[] args) { //stdlib.Trace.graphvizShowSteps (true); stdlib.Trace.run (); System.out.println(new Pair<>(42, "dog")); } }

file:Pair.java [source] [doc-public] [doc-private]

01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 package basics.immutabledata; final public class Pair<S extends Comparable<S>, T extends Comparable<T>> implements Comparable<Pair<S,T>> { final private S x; final private T y; public Pair(S x, T y) { if (x == null || y == null) throw new IllegalArgumentException(); this.x = x; this.y = y; } public S first() { return x; } public T second() { return y; } public String toString() { return "Pair(" + x + "," + y + ")"; } public boolean equals(Object thatObject) { if (thatObject == null) return false; if (this == thatObject) return true; // equals should not throw ClassCastException if (!(this.getClass().equals(thatObject.getClass()))) return false; @SuppressWarnings("unchecked") Pair<S,T> that = (Pair<S,T>) thatObject; return x.equals(that.x) && y.equals(that.y); } private int hcode; public int hashCode() { if (hcode == 0) { hcode = 17; hcode = 37*hcode + x.hashCode(); hcode = 37*hcode + y.hashCode(); } return hcode; } public int compareTo(Pair<S,T> that) { // compareTo may throw ClassCastException int ix = x.compareTo(that.x); if (ix != 0) return ix; return y.compareTo(that.y); } }