Getting ready

The Objects class has only 17 methods, all of which are static. For a better overview, we have organized them into seven groups:

• compare(): One method compares two objects using the provided Comparator
• toString(): Two methods that convert an Object to a String value
• checkIndex(): Three methods that allow us to check whether the index and the length of a collection or an array are compatible
• requireNonNull(): Five methods throw an exception if the provided object is null
• hash(), hashCode(): Two methods that calculate a hash value for a single object or an array of objects
• isNull(), nonNull(): Two methods that wrap the obj == null or  obj != null expressions
• equals(), deepEquals(): Two methods that compare two objects that can be null or arrays

We are going to write code that uses these methods in the preceding sequence.