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  1. import java.util.*;
  2. import java.lang.*;
  3. import java.io.*;
  4.  
  5. abstract class A
  6. {
  7. 	final int value;
  8. 	protected A(int value) { this.value = value; }
  9. 	public int hashCode() { return value; }
  10. 	public boolean equals(Object o) {
  11. 		if (o == this) return true; if (o == null) return false;
  12. 		if (!(o instanceof A)) return false;
  13. 		return value == ((A)o).value; // ? extend A class???
  14. 	}
  15. }
  16.  
  17. class B extends A {
  18. 	final String name;
  19. 	public B(int value, String name) { super(value); this.name = name; }
  20. 	public int hashCode() { return name.hashCode() ^ super.hashCode(); }
  21. 	public boolean equals(Object o) {
  22. 		if (!super.equals(o)) return false;
  23. 		if (!(o instanceof B)) return false;
  24. 		return name.equals(((B)o).name); // ? extend B class???
  25. 	}
  26. }
  27.  
  28. class C extends A {
  29. 	public C(int value) { super(value); }
  30. 	// really need to override method equals
  31. }
  32.  
  33. abstract class X
  34. {
  35. 	final int value;
  36. 	protected X(int value) { this.value = value; }
  37. 	public int hashCode() { return value; }
  38. 	public boolean equals(Object o) {
  39. 		if (o == this) return true; if (o == null) return false;
  40. 		if (o.getClass() != getClass()) return false;
  41. 		return value == ((X)o).value;
  42. 	}
  43. }
  44.  
  45. class Y extends X {
  46. 	final String name;
  47. 	public Y(int value, String name) { super(value); this.name = name; }
  48. 	public int hashCode() { return name.hashCode() ^ super.hashCode(); }
  49. 	public boolean equals(Object o) {
  50. 		if (!super.equals(o)) return false;
  51. 		return name.equals(((Y)o).name); // depend calling getClass in super.equals
  52. 	}
  53. }
  54.  
  55. class Z extends X {
  56. 	public Z(int value) { super(value); }
  57. 	// depend calling getClass in super.equals
  58. }
  59.  
  60. class Ideone
  61. {
  62. 	static void println(Object o) { System.out.println(o); }
  63. 	public static void main (String[] args) throws java.lang.Exception
  64. 	{
  65. 		A a1 = new B(123, "hoge");
  66. 		A a2 = new B(123, "hoge");
  67. 		A a3 = new C(123);
  68. 		A a4 = new C(123);
  69.  
  70. 		println("a1 == a2 (want true): " + a1.equals(a2));
  71.  
  72. 		println("a1 == a3 (want false): " + a1.equals(a3));
  73.  
  74. 		println("a3 == a1 (want false): " + a3.equals(a1));
  75.  
  76. 		println("a3 == a4 (want true): " + a3.equals(a4));
  77.  
  78. 		println("---------");
  79.  
  80. 		X x1 = new Y(123, "hoge");
  81. 		X x2 = new Y(123, "hoge");
  82. 		X x3 = new Z(123);
  83. 		X x4 = new Z(123);
  84.  
  85. 		println("x1 == x2 (want true): " + x1.equals(x2));
  86.  
  87. 		println("x1 == x3 (want false): " + x1.equals(x3));
  88.  
  89. 		println("x3 == x1 (want false): " + x3.equals(x1));
  90.  
  91. 		println("x3 == x4 (want true): " + x3.equals(x4));
  92. 	}
  93. }
Success #stdin #stdout 0.03s 320576KB
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stdin
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Standard input is empty
stdout
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a1 == a2 (want true): true
a1 == a3 (want false): false
a3 == a1 (want false): true
a3 == a4 (want true): true
---------
x1 == x2 (want true): true
x1 == x3 (want false): false
x3 == x1 (want false): false
x3 == x4 (want true): true
https://ideone.com/AVIrGh
language:
Java (HotSpot 12)
created:
7 years ago
visibility:
public

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