C:\Program Files\Research In Motion\BlackBerry JDE 4.7.0).Enter BlackBerry as Platform Name.cmd /C "cd /D {platformhome}{/}simulator&{device}"cmd /C "cd /D {platformhome}{/}bin&jdwp"net_rim_api.jar and click Remove. Click Next.net_rim_api.jar is not in the list, Click the Add button, and type in or navigate to C:\Program Files\Research In Motion\blackberry JDE 4.7.0\lib\net_rim_api.jar and click Open. C:\Program Files\Research In Motion\BlackBerry JDE 4.7.0\docs\api\. | 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. |
| * The scope of an automatic variable is method scope and the member variable life is class level. * Protected features are available to class, subclass, within a package and only for subclasses in a different package. * If you don't specify an access modifier, then compiler assigns default access modifier, which is not a keyword. * A 'final' variable must be initialized at the point of declaration. * If define a class as final then the class cannot be extended (avoiding the inheritance). * An abstract classes cannot be instantiated. If you define one method as abstract in a class the class must be defined as abstract. * If you define one non default constructor in any given class, then the default constructor will not be provided by the compiler. |
In the declaration of a field, setting it explicitly to its default initial value is always redundant, and may even cause the same operation to be performed twice (depending on your compiler). |
Declaring and initializing object fields as null, for instance, is simply not necessary in Java. |
public final class Quark { //WITH redundant initialization to default values private String fName = null; private double fMass = 0; public Quark(String aName, double aMass){ fName = aName; fMass = aMass; } } The correct approach would be - public final class Quark { //WITHOUT redundant initialization to default values private String fName ; private double fMass ; public Quark(String aName, double aMass){ fName = aName; fMass = aMass; } } |