Java simplified

Java programs are either Applets or Applications. The first one runs under an HTML environment in a browser window, the later runs standalone like we are used to thinking about how programs run. Most of the commands and features available to one are available to the other. Obviously Applets, since they are running on someone's computer anywhere in the world must have some restrictions (e.g.. cannot modify files on someone's computer) Most of the standard commands and control statements in Java are quite similar to those of other languages. Assignment statements, if statements, for-next statements, Do - While statements, etc. are easy to understand and pretty similar in most languages. However , using these statements to accomplish some logical end is the first stumbling block that beginning programmers need to overcome. Understanding the various data types both primitive and non primitive is of major importance to Java programmers. Primitive types are pretty obvious and used in most languages on an everyday basis. Such types are : int long short double float char Boolean etc. Non primitive types are referred to as reference variables because they point to memory locations that contain the values. Strings etc. In addition to the above another important learning step is how to organize our program so that it will work. Concepts such as top-down, or styles that use a modular approach are quite popular. Modular means to divide the logic into sections of code and then call each section as it is needed. Think of modules are being small programs. These small programs can also be called function or even METHODS. Remember that when you use them , their purpose is to perform some task. Understanding the concept of Methods is critical to appreciating the power of Java. In addition to Methods performing tasks (just like a program, they can receive values (to play with) and return results (if needed). So in short programs are groups of Methods and variables interacting. In Java we will refer to this grouping as CLASSES. So instead of writing programs we are really writing CLASSES. And each of our Classes contains METHODS (or member function) to perform specific tasks. Now the real power explained. People have written many CLASSES already. These CLASSES perform a wide range of tasks for you , so you in essence do not have to reinvent the wheel every time you need something. These CLASSES are bundled together into PACKAGES , which you import into your program (at the top). Common packages are java.awt or java.lang or java.applet etc. New CLASSES are being developed all the time. Bundled into packages and made available to the programmer. (java.swing is an example from our textbook). So in short you are not writing programs, you are writing classes that can use existing classes to help them achieve their goals When your class needs something that another class has to offer you can normally do one of two things after the import of the package containing the class: 1.. directly refer to a member function in that class to perform the task String name = JOptionPane.showInputDialog("enter your name " ) 2.. create an OBJECT of that class and then refer to the object along with the member function so the task can be performed Button red = new Button(); .... red.setBounds (1,2,44,23); In summary the full power of java and object oriented programming is realized when our class creates objects of existing classes which were created from other classes. Classes can inherit the capabilities and power of the classes from which they were derived and so on and so on. So not only are we not reinventing the wheel , we are pulling a wheel of the shelf that is already fine tuned and using that to go forward to design yet even better classes to solve problems. When designing our own classes there are way to allow access to certain methods and variables and not allow access to others. In other words we allow enough access to realize its power but not enough to mess it up. I will spend more time on these and other concepts later.

Sorting Arrays

// Interchange sort high to low // assume n[] is 10 big and it contains 10 numbers and is 'int' // compares each element with each one under it // visualize it as 9 sorts on an array that is getting smallerint g,r,c; for ( r=0; r <=8; r++)    {      for ( g=r+1;g<=9;g++)         {             if ( n[r]  < n[g] )                {                    c=n[r];                // these 3 statements swap values                    n[r] = n[g];          // in the 2 cells being compared                     n[g] = c;                 }         }      }  // bubble sort on the same array above // compares pairs of elements during a pass // an element can only move up one spot each pass // finished if nothing was swapped or at most n-1 passes int sw,r,c,g; do    {    sw = 0;     for ( r=0; r <=8; r++)       {         g=r+1;         if (n[r] <  n[g] )           {              c=n[r];              // next 3 statements swap 2 values              n[r] = n[g];              n[g] = c;              sw=1;           }       }     }  while ( sw = 1 } // QUICK SORT is coming soon // Sorting using pointer technique is coming

Variable Types

Variable Types

Since Variables stand for items that the program is manipulating or playing with,  such as:                         whole numbers       (small  normal   large)                         fractional numbers        (small   large)                         single characters                         groups of characters as a unit                          true / false conditions  it is only logical to assume that JAVA gives the programmer  the  capability to declare and use Variables that can hold each of the above data types.  Remember that values ( or data ) being put into Variables is the heart or basis of programming.  Variables MUST be declared before they can be used in a program. Common Variable types are as follows:    short                     ... small integers    int                          ... normal integers    long                       ... big integers    float                       ... small fractional numbers    double                   ... big fractional numbers     char                       ... single character values   e.g.,     M    or   F    string                     ... groups of characters viewed as a unit    Boolean                 ... logical  TRUE  or  FALSE  values  In object oriented and more sophisticated programs today, the programmer can declare his or her own data type ( later ) Specifics concerning Java Data TYpes NUMERIC (all numbers are signed) short integer (16 bit number) --> i.e. 32,768 int integer (32 bit number) --> i.e. 2 billion or 2 x 109 long integer (64 bit number) --> i.e. 9 x 1018 float real (32 bit decimal) --> i.e. 1.4 x 10-45 to 3.4 x 1038 double real (64 bit decimal) --> i.e. 4.9 x 10-324 to 1.7 x 10308   CHARACTER / STRING char a unicode (2-byte) char the String class handles multi-character strings (strings are unicode, as well). Strings are said to be immutable: updates to a String cause the new string to be created in memory (and pointed to by the String class). However the old string is not actually "updated", rather, its reference is lost (and it becomes available for garbage collection).   BOOLEAN boolean (with values true, false)   DATE the Date class measures the milliseconds since Jan 1, 1970 and provides supporting functions to interpret and manipulate date/times   ARRAYS arrays hold multiple instances of a data type or object

Programming Tuturials

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Sorting an Array

Hello programmers.. my students.. i want to create a program in java that sort a number in descending order.

here is a sample program...
public class Sorting
{
    public static void main(String args[])
    {
        int arr[]={0,1,2,3,4,5,6,7,8,9,10};
        int temp=0;
       
        for(int i=0; i<10;i++)
        {
            for(int j=0; j<10; j++)
            {
                if(arr[j]
                {
                    temp=arr[j];
                    arr[j]=arr[j+1];
                    arr[j+1]=temp;
                }
            }
        }
       
        for(int x=0; x<10; x++)
        {
            System.out.println(arr[x]+ " ");
        }
    }
}

i hope you learn more in my blog,.... Think it Code it

Programming Tuturials

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http://webpages.shepherd.edu/JROMANO/arrays.htm

Array Definition and samples

An array is multiple storage locations under one name. For now
we will talk about one and two dimensional arrays.

All the primitive data types that we have learned and used concerning
regular variables also apply to arrays.

int num = new int; // declare / initialize an integer variable

int nums[] = new int [10]; // declare and allocate space for 10 integer
// numbers. The 10 elements have the same
// name but each one will be referred to
// with a different subscript or position
// in the array. Thos array contains 10
// integer locations, number 0 thru 9

Anything that you can do with an integer variable, you can do with
each element of an integer array. But you must indicate which element
you are referring to.

e.g.. nums[0]=100;
nums[5]=200; etc.
JOptionPane.showMessageDialog(null,"answer is "+nums[2]);

Loops make working with arrays very easy.

for example:
int tot=100;
int n=0;
do
{
nums[n] = tot;
n=n+1;
} while (n <= 9 );

Remember that all rules that apply to variables of a specific type
also apply to each element of an array of that type.

Two dimensional arrays adhere to all the rules noted above, except
any reference to a two dimensional array must have 2 subscripts.

int numbers[] [] = new int [5] [10];

The above array has 5 rows and 10 columns.
The rows are numbered 0 thru 4, and the columns are numbered 0 thru 9.


Any reference to the array will have 2 subscripts and the first one will be
the row and the second one will be the column.

e.g.. numbers[1][3] = 100;

Loops are very useful with two dimensional arrays just like one
dimensional arrays, but a lot of the times nested loops are used
because of the nature of two dimensional arrays.

e.g.. int tot=10;
for(int a=0;a<=4;a++)
{
for(int b=0;b<=9;b++)
{
numbers[a][b] = tot;
tot=tot+10;
}
}

.
arrays can be declared but still need to be explicitly initialized
int [] dataPoints; // declares the array of integer
dataPoints = new int[10] ; // allocates array size (now usable)
dataPoints = new int[numPoints]; // allocates array size with size specified by a run-time variable
an array can be re-initialized (with the same data type) at runtime, at which point old array entries are discarded
Java standard arrays cannot are not dynamically resizable like arrays in Visual Basic or PowerBuilder (i.e. where the language can dynamically extend the array, if needed). Java throws an exception if an out-of-bounds array index is referenced. Java.util's Vector class provides dynamic array-like capability (a Vector can store a collection of any type of object). The standard Vector class does not, however, limit data to a specific data type (data type limitation capability has to be built in a Vector extension).