Interview ready notes on java.lang and java.util packages

The java.lang Package.     * Math class is defined as final class and its constructor is defined as private that is why you cannot extend and you cannot instantiate Math class.     * Math.random() returns a random number between 0.0 and 1.0.     * The method Math.ceil(double db) returns a double value the smallest whole number greater than or equals to db.     * The method Math.floor(double d) returns a double value the largest whole number less than or equal to db.     * In Java Strings are immutable.     * You can use either "==" or Object.equals() method to compare two string objects.     * The "==" is used to compare whether two references are pointing to same object or not ( call hallow comparison ).     * The Object.equals() method compares two string objects character by character ( called deep comparison ).     * String objects created with String and StringBuffer class cannot be compared for equality ( returns false ). The java.util Package.     * A simple collection places no constraints on type of elements, order of elements , repetition of elements within the collection.     * The collection interfaces are Collection, List, Set, and Map.     * The java.util.List interface insists ordering and allows duplicates.     * The java.util.Set interface eliminates duplicate values and implemented in HashSet and TreeSet classes in collections framework.     * If you try to add duplicates in a collection ( Set collection ), the Set.add() method  returns false.     * In Set interface implementations if null is valid entry , it should appear only one time     * The TreeSet class provides ordered set and uses tree for storage.     * The TreeMap provides ordered map.     * The size of the Vector grows or shrinks depends on the number of elements are getting added or removed. It uses internally array for storage.     * A Stack is subclass of Vector that implements a standard last-in, first-out stack.     * The Enumeration interface defines the methods by which you can enumerate the elements in a collection of objects.     * A BitSet is a really a vector of bits and is used if you want to efficiently store a lot of on-off information.