how to generate barcode in vb.net 2008 Understanding Primitives, Enumerations, and Objects in Java

Creation Code39 in Java Understanding Primitives, Enumerations, and Objects

Understanding Primitives, Enumerations, and Objects
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int[] intArray = new int[4]
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int[0] int[1] int[2] int[3]
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array declaration
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Arrays are useful in loops. It is very common to access an array in a loop with a variable as the index. This variable would be incremented each time through the loop until the end of the array. The developer must take caution not to use an index that is out of bounds. An out of bounds index will cause the Java Virtual Machine to throw an exception at runtime. Once the size of an array is set, it cannot be changed. This makes arrays less useful in situations where the data set may grow. Figure 4-1 shows a basic array declaration.
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Remember that an array is an object. On the SCJA exam, they may ask how many objects are referenced in a code segment, and try to throw you off by having an array of primitives. Even if it is an array of primitives, it is still an object.
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Enumerations are a special data type in Java that allows for a variable to be set to predefined constants. The variable must equal one of the values that have been predefined for it. An enumeration is useful when there is a limited set of options that a variable can equal and it is restricted to these known values. For example, a deck of playing cards will always have four suits: clubs, diamonds, hearts, and spades. If a developer wanted to represent a card, an enumeration could be used to represent the suit.
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enum Suit { CLUBS, DIAMONDS, HEARTS, SPADES }
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The preceding is an example of an enumeration that would be used to store the suit of a playing card. It is defined with the keyword enum. The enum keyword is used in the same manner as the class keyword. It can be defined in its own Java file, or embedded in a class.
Suit cardSuit; cardSuit = Suit.CLUBS; if(cardSuit == Suit.CLUBS){ System.out.println("The suit of this card is clubs."); }
4:
Working with Basic Classes and Variables
The preceding example demonstrates an enumeration being used. The variable card is declared as a Suit. Suit was defined earlier as an enumeration. The cardSuit variable can now be used to store one of the four predefined suit values.
Benefits of Using enumerations
An object can be created to work in the same manner as enumerations. In fact, enumerations were not even in the Java language until version 5.0. However, enumerations make code more readable and provide less room for programmer error.
Java Is strongly typed
Java is a strongly typed programming language. Java requires that a developer declare the data type of each variable they use. Once a variable is declared as one type, all data stored in it must be compatible with that type. Think back to the primitive data types we reviewed previously. For example, once a variable is declared as an int, only int data can be stored within it. Data can be converted from one type to another. This will be discussed later in this section.
Understanding strongly typed Variables
Strongly typed variables help to create more reliable code. In most cases, the Java compiler will not allow the developer to inadvertently store mismatched data types. Only variables with the same data type are compatible with each other. For example, a float cannot be stored in any other data type other than a float. The same is true for all primitives and objects. The Java Virtual Machine will do some automatic conversions for the developer. It is important to understand that the types are not compatible and that the code will only work because of the conversion that is happening. An example of a conversion would be going from an int to a float. The Java Virtual Machine will allow for an int to be placed into a float because it can convert an int to a float without losing precision. The converse is not true. A float cannot be converted to an int without the loss of precision.
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