Home : Course Map : Chapter 2 : Java :
Essential Elements and Structures
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Chapter 2

Introduction
Essentials
Structure

Keywords
Primitive Types
Comments
Literals
Expressions
Operators
Statements
Casts & Mixing
Strings
Console Output 
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Exercises

    Supplements
Conditional: if-else
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Like any computer language, Java consists of a set of basic set of elements, such as keywords and symbols. It combines these elements into small substructures such as expressions and statements. These substructures in turn create the larger structures called methods and classes.

Basic Elements

These essential elements of Java include:

  • Keywords & Symbols

    The programmer has wide latitude for the names of variables and classes but Java reserves some words for itself. These keywords include, for example,

       
    class, float, return, if, else

    See the Table of Keywords for the complete list of reserved words and the Table of Reserved Symbols

  • Data types

    Java represents different types of basic data and what operations the data types can undergo. Eight keywords specify the eight kinds of basic data, which are referred to as primitives. These are

        byte, short, int, long - integers
        float, double
    - floating point
        boolean - logical true/false
        char
    - 2 byte Unicode characters and
              can also act as 2 byte unsigned integers


    Much more about primitives later.

  • Operators

    Java has arithmetic operators (+, -, /, * ,%), boolean operators (&, |, etc.), comparisons (==, <=, etc.) and others. A complete listing is given in the Tables of Operators

  • Identifiers

    Identifiers are the names given to data, methods and classes. Java is a strongly typed language, meaning that you must declare the particular type to which a datum belongs. Identifiers cannot begin with a number and an identifier cannot contain a punctuation character or any character listed in the Reserved Symbols Table. Underscore _ and the dollar sign $ are allowed.

    The types of variables include:

    • Primitive type variables

       int n = 5;  // n is an integer variable
       double x;   // x is a double type identifier
                   // not explicitly initialized.


    • Reference variables - specify an object

       String x = "foo"; // x references the string object.

    • Array variables

       x = b * iArray[5]; // element 5 in iArray is specified

  • Literals

    A specific primitive value in a line of code is called a literal. These will be translated into values by the compiler and inserted into the byte code.

      int i = 3;      // 3 is an integer literal
      double x = 4.0; // 4.0 is a double type literal
      long l = 12L;   // long literals must be specified with L
      float f = 1.2f; // float literals must be specified with f

Language Structures

The above building blocks then combine into the following higher level components to express instructions :

  • Expressions

    An expression contains an operation on one or more operands that returns a value. In some cases it also changes an operand.

        x = 5   // assignment operation
        y < 5   // comparison operation
        14. * y // multiplication operation


  • Statements
    Composed of one or more expressions, a statement is a complete action to execute:

        
    x = 5;
        if (y < 5) x= 3;
        return (x = 3.0 * (14.0 * y);


Finally, these components fit within the structure of a class and its member fields and methods (methods are Java's version of the subroutines and functions in other languages). We will discuss Java classes and objects in Chapter 3 but for now you can program within the class framework without understanding its details.

The generic program in the following section illustrates the basic structure of a Java program.

Latest update: Oct. 13, 2004

            Tech
Arithmetic Ops
Math Class
More on Integers
FP : Overview
FP : Java  
  
Demo 1
More Mix/Cast
  Demo 2
Exercises

           Physics
Differential Eq.
Euler Method
  
Demo 1
Predictor-Corrector
  
Demo 2
Exercises

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