if (myString != null && !myString.isEmpty()) { // doSomething } As further comment, you should be aware of this term in the equals contract: From Object.equals(Object): For any non-null reference value x, x.equals(null) should return false. The way to compare with null is to use x == null and x != null. Moreover, x.field and … Read more
To answer the precise question “Why doesn’t Set provide an operation to get an element that equals another element?”, the answer would be: because the designers of the collection framework were not very forward looking. They didn’t anticipate your very legitimate use case, naively tried to “model the mathematical set abstraction” (from the javadoc) and … Read more
If you’re looking for efficiency, use this: string.Equals(val, “astringvalue”, StringComparison.OrdinalIgnoreCase) Ordinal comparisons can be significantly faster than culture-aware comparisons. ToLowerCase can be the better option if you’re doing a lot of comparisons against the same string, however. As with any performance optimization: measure it, then decide!
Hibernate has a nice and long description of when / how to override equals() / hashCode() in documentation The gist of it is you only need to worry about it if your entity will be part of a Set or if you’re going to be detaching / attaching its instances. The latter is not that … Read more
The string constant pool will essentially cache all string literals so they’re the same object underneath, which is why you see the output you do for s1==s2. It’s essentially an optimisation in the VM to avoid creating a new string object each time a literal is declared, which could get very expensive very quickly! With … Read more
Because “true” is converted to NaN, while true is converted to 1. So they differ. Like you reported, both are converted to numbers, because at least true can be (see Erik Reppen’s comment), and then compared.
You can not overload the == operator, but you can override equals(Object) if you want it to behave differently from the == operator, i.e. not compare references but actually compare the objects (e.g. using all or some of their fields). Also, if you do override equals(Object), have a look at hashCode() as well. These two … 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
//Written by K@stackoverflow public class Main { /** * @param args the command line arguments */ public static void main(String[] args) { // TODO code application logic here ArrayList<Person> people = new ArrayList<Person>(); people.add(new Person(“Subash Adhikari”, 28)); people.add(new Person(“K”, 28)); people.add(new Person(“StackOverflow”, 4)); people.add(new Person(“Subash Adhikari”, 28)); for (int i = 0; i < people.size() … 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