Java OCA OCP Practice Question 2853

Question

Given: 

2. class Square {  
3.   Square(String c, int h) { color = c; hotness = h; }  
4.   String color;  //from www. j ava 2  s . c  o m
5.   private int hotness;  
6.   public boolean equals(Object o) {  
7.     Square c = (Square)o;  
8.     if(color.equals(c.color) && (hotness == c.hotness))  return true;  
9.     return false;  
10.   }  
11.   // insert code here  
12. }

Which, inserted independently at line 11, fulfill the equals() and hashCode() contract for Square? (Choose all that apply.).

  • A. public int hashCode() { return 7; }
  • B. public int hashCode() { return hotness; }
  • C. public int hashCode() { return color.length(); }
  • D. public int hashCode() { return (int)(Math.random() * 200); }
  • E. public int hashCode() { return (color.length() + hotness); }


A, B, C, and E are correct.

Note

They all guarantee that two objects that equals() says are equal, will return the same integer from hashCode().

The fact that hotness is private has no bearing on the legality or effectiveness of the hashCode() method.

D is incorrect because the random() method will usually return different integers for two objects that equals() says are equal.

E is correct.

Of all the legal hashCode() methods, this one will create the most hash buckets, which will lead to the fastest retrieval times.




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