//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
There’s no difference, == is a synonym for = (for the C/C++ people, I assume). See here, for example. You could double-check just to be really sure or just for your interest by looking at the bash source code, should be somewhere in the parsing code there, but I couldn’t find it straightaway.
In Java, the equals() method that is inherited from Object is: public boolean equals(Object other); In other words, the parameter must be of type Object. This is called overriding; your method public boolean equals(Book other) does what is called overloading to the equals() method. The ArrayList uses overridden equals() methods to compare contents (e.g. for … Read more
The commons/lang builders are great and I have been using them for years without noticeable performance overhead (with and without hibernate). But as Alain writes, the Guava way is even nicer: Here’s a sample Bean: public class Bean{ private String name; private int length; private List<Bean> children; } Here’s equals() and hashCode() implemented with Commons/Lang: … Read more
IEqualityComparer<T> is an interface for an object that performs the comparison on two objects of the type T. IEquatable<T> is for an object of type T so that it can compare itself to another of the same type.
You may also understand the difference between null and an empty string this way: Original image by R. Sato (@raysato)
The answer is in the JavaDoc of the equals() method: 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). In other words: equals() checks if the BigDecimal objects are exactly the same in every … Read more
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
Josh Bloch favors your approach: The reason that I favor the instanceof approach is that when you use the getClass approach, you have the restriction that objects are only equal to other objects of the same class, the same run time type. If you extend a class and add a couple of innocuous methods to … Read more
The main reason is performance. When generics were introduced in .NET 2.0 they were able to add a bunch of neat classes such as List<T>, Dictionary<K,V>, HashSet<T>, etc. These structures make heavy use of GetHashCode and Equals. But for value types this required boxing. IEquatable<T> lets a structure implement a strongly typed Equals method so … Read more