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The Java super class java.lang.Object has two very important methods defined in it. They are -

• public boolean equals(Object obj)
  
• public int hashCode()
  

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1. public class Test
2. {
3. private int num;
4. private String data;
5.
6. public boolean equals(Object obj)
7. {
8. if(this == obj)
9. return true;
10. if((obj == null) || (obj.getClass() != this.getClass()))
11. return false;
12. // object must be Test at this point
13. Test test = (Test)obj;
14. return num == test.num &&
15. (data == test.data || (data != null && data.equals(test.data)));
16. }
17.
18. public int hashCode()
19. {
20. int hash = 7;
21. hash = 31 * hash + num;
22. hash = 31 * hash + (null == data ? 0 : data.hashCode());
23. return hash;
24. }
25.
26. // other methods
27. }