- OVERRIDING EQUALS METHOD MAP HOW TO
- OVERRIDING EQUALS METHOD MAP CODE
If the value of the field is null, return 0.
If the field is an array, invoke the Arrays.hashCode() method or compute hashCode for each array element by applying the above rules. Recursively invoke hashCode on the field that is an object reference. (int)(f ^ (f > 32)) for a long ( > is unsigned right shift operator) and Float.floatToIntBits(f) and Double.doubleToLongBits(f), for float and double, respectively. For primitive fields, compute (int)f for byte, char or short, (f ? 1 : 0) for a boolean,. 
For all relevant fields from the object (which are used in the equals method for equality), compute the hashcode c by the following rules and append c into the result using prime multiplier 37 as result = 31 * result + c. Initialize hashcode by a nonzero value ideally, a prime number, say 17.Ģ. Here’s the recommended process to compute hashCode manually before Java 7:ġ. Now let’s discuss various ways to override the equals() and hashCode() methods in Java.
If equals() returns false for two objects, then hashCode() method should return different values, i.e., if a.equals(b) = false or b.equals(a) = false, then a.hashCode() != b.hashCode(). If equals() returns true for two objects, then hashCode() method should also return the same value, i.e., if a.equals(b) = true and b.equals(a) = true, then a.hashCode() = b.hashCode(). Otherwise, the class object will not behave properly on hash-based collections like HashMap, HashSet, and Hashtable (see why?). Item 9 in Josh Bloch’s Effective Java always asks us to override the hashCode() method if the class overrides equals(). Consistent: Multiple calls to equals ( x.equals(y) or y.equals(x)) must return the same value at any point of time unless either x or y is modified. Transitive: If the first object is equal to a second object and the second object is equal to a third object, then the first object should be equal to the third object, i.e., x.equals(y) = true and y.equals(z) = true, then x.equals(z) = true. Symmetric: If the first object is equal to a second object, then the second object should be equal to the first object, i.e., x.equals(y) = true if and only if y.equals(x) = true. OVERRIDING EQUALS METHOD MAP CODE
Following is the piece of code of equals()method from Objectclass. So you have to override the equals() method, replacing it with your own. It does not make member level comparison. Recall that an abstraction function f: R A maps concrete instances of a data. Reflexive: A non-null object should be equal to itself, i.e., x.equals(x) = true. In order to compare two objects for equality, we need to override equals()method because it is originally defined in Objectclass that takes a parameter of type Objectand compares it with thisreference.Ideally equals() method should satisfy the following conditions. The general contract for overriding equals is proposed in item 8 of Josh Bloch’s Effective Java.
OVERRIDING EQUALS METHOD MAP HOW TO
This post will discuss how to override equals() and hashCode() methods in Java.
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