001package algs34; 002import stdlib.*; 003import java.util.HashSet; 004 005public final class XGoodPoint { 006 static class GoodPoint { 007 private final double x; 008 private final double y; 009 public GoodPoint(double x, double y) { this.x = x; this.y = y; } 010 public String toString() { return "(" + x + ", " + y + ")"; } 011 012 public boolean equals(Object other) { 013 if (other == this) return true; 014 if (other == null || other.getClass() != this.getClass()) return false; 015 GoodPoint that = (GoodPoint) other; 016 if (Double.compare(this.x,that.x) != 0) return false; 017 if (Double.compare(this.y,that.y) != 0) return false; 018 return true; 019 } 020 public int hashCode() { 021 int h = 17; 022 h = 31*h + Double.hashCode(x); 023 h = 31*h + Double.hashCode(y); 024 return h; 025 } 026 } 027 028 029 public static void main(String[] args) { 030 GoodPoint a = new GoodPoint(0.0, 0.0); 031 GoodPoint b = new GoodPoint(0.0, 0.0); 032 GoodPoint e = new GoodPoint(0.0,-0.0); 033 StdOut.format("a = %s [hashcode=%d]\n", a, a.hashCode ()); 034 StdOut.format("b = %s [hashcode=%d]\n", b, b.hashCode ()); 035 StdOut.format("e = %s [hashcode=%d]\n", e, e.hashCode ()); 036 037 HashSet<GoodPoint> set = new HashSet<>(); 038 set.add(a); 039 StdOut.println("Added a"); 040 StdOut.println("a == b: " + (a == b)); 041 StdOut.println("a.equals(b): " + (a.equals(b))); 042 StdOut.println("contains b: " + set.contains(b)); 043 StdOut.println("a == e: " + (a == e)); 044 StdOut.println("a.equals(e): " + (a.equals(e))); 045 StdOut.println("contains e: " + set.contains(e)); 046 } 047}