How does that work if the fields that it’s based on are mutable? It doesn’t in the sense that the hash code will change as the object changes. That is a problem for all of the reasons listed in the articles you read. Unfortunately this is the type of problem that typically only show up … Read more
Yes it is possible to do such a thing. (And people have done it.) But it won’t allow you to put your objects into a HashMap, HashSet, etc. That is because the standard collection classes expect the key objects themselves to provide the equals and hashCode methods. (That is the way they are designed to … Read more
HashMap uses hashCode(), == and equals() for entry lookup. The lookup sequence for a given key k is as follows: Use k.hashCode() to determine which bucket the entry is stored, if any If found, for each entry’s key k1 in that bucket, if k == k1 || k.equals(k1), then return k1‘s entry Any other outcomes, … Read more
If the compile-time type of enumInstance is the enum type, you’re fine with ==. If the compile-time type of enumInstance is Enum, ValueType or Object, you need to use Equals. (You’ll get a compile-time error if you try to use == in that case.) Note that your enum currently violates .NET naming conventions – it … Read more
It sounds like you want to force your classes to override the default implementations of those methods. If so, the way to do this is to declare an abstract superclass that has the methods declared as abstract. For example: public abstract class MyBaseClass implements … /* existing interface(s) */ { public abstract boolean equals(Object other); … Read more
From the javadoc of BigDecimal equals public boolean equals(Object x) Compares this BigDecimal with the specified Object for equality. Unlike compareTo, this method considers two BigDecimal objects equal only if they are equal in value and scale (thus 2.0 is not equal to 2.00 when compared by this method). Simply use compareTo() == 0
Nice question, the surprising thing about the code above is that println “${‘test’}”.equals(‘test’) returns false. The other line of code returns the expected result, so let’s forget about that. Summary “${‘test’}”.equals(‘test’) The object that equals is called on is of type GStringImpl whereas ‘test’ is of type String, so they are not considered equal. But … Read more
Think of ! (negation operator) as “not”, || (boolean-or operator) as “or” and && (boolean-and operator) as “and”. See Operators and Operator Precedence. Thus: if(!(a || b)) { // means neither a nor b } However, using De Morgan’s Law, it could be written as: if(!a && !b) { // is not a and is … Read more
In Kotlin 1.1 you can use contentEquals and contentDeepEquals to compare two arrays for structural equality. e.g.: a contentEquals b // true b contentEquals c // false In Kotlin 1.0 there are no “built-in functions to the Kotlin std-lib that tests two arrays for (value) equality for each element.” “Arrays are always compared using equals(), … Read more
Yes. In Ruby the not equal to operator is: != You can get a full list of ruby operators here: https://www.tutorialspoint.com/ruby/ruby_operators.htm.