![]() So, for example, if the hashcode equals zero, the HashTable places the value into Bucket 0. #Compareto method map java code#The HashTable uses that code to determine the bucket in which to place the key/value. When you pass a key/value to the HashTable, it queries the key’s hashcode. The HashTable uses the key’s hashcode to determine to which bucket the key/value pair should map.Ībove image shows a HashTable and its buckets. A HashTable internally contains buckets in which it stores the key/value pairs. The hashCode() method of objects is used when you insert them into a HashTable, HashMap or HashSet.Ī slightly more in-depth explanation will help in understanding HashTable’s mechanism for storage and retrieval. Hence, we should always use equals() for value comparison. For the last two cases, we create separate String objects and hence the reference equality fails. JVM does not create a separate holder, but reuses the holder having same value from the String-pool. Now for third and fourth case, the string references are equal because their values are equal. The second case, the comparison is happening between two addresses in memory ( reference equality) and hence it returns false, even though the values are same. In the above example, the first output is a Java primitive type reference comparison between primitive types using ‘=’, compares their values. Check the below code : int a = 4 int b = 4 (a=b) Integer a1 = new Integer(2) Integer b1 = new Integer(2) (a1=b1) String a2 = "as" String b2 = "as" (a2=b2) (a2.equals(b2)) String a3 = new String("as") String b3 = new String("as") (a3=b3) (a3.equals(b3)) // Output: true false true true false true Now an important point to discuss in this context is the difference between reference equality and object equality. Note: You need not perform a null check since null instanceof EffectiveEqualswill evaluate to false.įinally, for Step 5, go back to equals()'s contract and ask yourself if the equals()method is reflexive, symmetric, and transitive. Here's the recipe in code form: public class EffectiveEquals Joshua Bloch offers a five-step recipe for writing an effective equals() method. For any non-null reference value x, x.equals(null) should return false.It is consistent: For any reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the object is modified.It is transitive: For any reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.It is symmetric: For any reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true. ![]()
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