Fundamental Programming Concept

Data Types

Variable Declaration

Assignment Statement

Increment/Decrement Operators

Arithmetic Operators

Type Conversion

Constant

Strings

Data Types

Integer

  byte : 1 Byte (-128 to +127)

  short : 2 Byte (-32,768 to +32,767)

  int : 4 Byte (-2,147,483,648 to +2,147,483,647)

  long : 8 Byte (-9,000,000,000,000,000,000 to +9,000,000,000,000,000,000 )

Variable Declaration

Examples:    

int total;

     int count, sum;

     // declare and initialize

     int total = 0, count = 20;

     float unit_price = 57.25;

Java Keywords

abstract,  boolean,  break,  byte,  case,  catch,  char,  class,  continue,  default,  do,  double,  else,  extends,  false,  final,
  finally,  float,  for,  if,  implements,  import,  instanceof,  int , interface,  long,  native , new,  null,  package,  private,
  protected,  public,  return,  short,  static,  super,  switch,  synchronized,  this,  throw,  throws,  transient,  true,  try,  void, 
volatile,  while

Keywords that are reserved but not used by Java

          const,  goto

For Variable Declaration

Do not use Integer at the started

Do not use ? or %

Do not use spacebar

Do not use reserved words

Assignment Statements

Examples:

int x, sum = 0;

x = 10;

    x = x + 1;

    sum = sum + x;

Increment and Decrement Operators (++, --)

1.   prefix: ++n (increase the value of n before using n)
2.   postfix: n++ (increase the value of n after using n)

เช่น       n = 5;                          n = 5;
            x = n++;                       x = ++n;
          //  x = 5                   // x = 6
                n = 6                       n = 6              

1. (i+j)++;            ==>  illegal

Arithmetic Operators

+   -    *    /    %

A = 10 + 20 - 5 * 2;

X = 7.0 / 2.0        //    3.5

Y  = 7 / 2             //   Div => 3

Z = 3 % 5            //   Modulo => 3

Type Conversion

    double sum = “a lot”;         // Error 
------------------------------

    int baht = 2;

    double sum = baht;   // OK

    baht = (int) sum;       // Convert double to int

------------------------------

    sum = 13.75

    int p = (int) (sum * 100);   // => 1375

    int p = (int) sum * 100;      // => 1300

------------------------------

Constant

    final double PI = 3.14159;

    final int STUDENTS = 25;

STUDENTS = 30; // cannot change !!!

    x = Math.PI;  // constant in class Math

Math Class

Methods:

Math.abs( x ): Math.abs(-10) is 10

Math.ceil( x ): Math.ceil(9.2) is 10;
      Math.ceil(-9.8) is -9

Math.cos( x ): Math.cos(0.0) is 1

Math.exp( x ): Math.exp(1.0) is 2.71828

Math.floor( x ): Math.floor(9.2) is 9;
      Math.floor(-9.8) is -10

Math.log( x ): Math.log(2.718282) is 1

Strings

Strings Declaration
String name = “Jane”;

Assign Strings
name = “John”;

Strings length
int n = name.length();

Not String.length(name)

Empty string is Strings that has String length equals 0
String name = “”;

Substrings

String.substring(begin, end)

String s = “Hello World!”;
String sub = s.substring(0, 4);

The results of sub = “Hell”

The first index of Java Strings is 0

String m = s.substring(6, 11);
The results of m = “World”

String t = s.substring(6);   // “World!”

Concatenation

For concatenation we use +
String fname = “Peter”;
String lname = “Pan”;
String name = fname + lname;
      // We have got “PeterPan”

OR String name = fname + “  ”  + lname;
      // We have got “Peter  Pan”

Adding Strings with Integer,the result is Strings
String m = “Version”;
int n = 7;
String o = m + n;    // “Version7”

Convert Strings-Integer,Double

int age = 20;
String ages = Integer.toString(age); // “20”

double weight = 40.6;
String weights = Double.toString(weight); // “40.6”

String ages = “20”;
int age = Integer.parseInt(ages);  // 20

String prices = “$3.80”;
double p = Double.parseDouble(prices.substring(1));
      // 3.80

Exercise 1

Write a program that inputs three integer from the keyboard via command line and displays the sum, average, product, maximum, and minimum of the numbers.

Example StringEx1.java
public class StringEx1 {
                public static void main(String args[]) {
                     String name1 = "Chulalongkorn";
                     String name2 = "University";
                  
                     System.out.println("Name 1 = " + name1);
                     System.out.println("Length of Name 1 = " + name1.length());
                     String name3 = name1 + " " + name2;
                     System.out.println("Name 3 = " + name3);
                     String name4 = name1.substring(0, 5);
                     String name5 = name1.substring(5);
                     String name6 = name3 + " is the oldest university in Thailand";
                     System.out.println("Name 4 = " + name4);
                     System.out.println("Name 5 = " + name5);
                     System.out.println("Name 6 = " + name6);
                    
                     String data1 = "30";
                     String data2 = "45.60";
                     int n1, n2;
                     double n3, n4;
                     n1 = Integer.parseInt(data1);
                     n2 = n1 + 20;
                     System.out.println("n2 = " + n2);
                     n3 = Double.parseDouble(data2);
                     n4 = n3 + 54.40;
                     System.out.println("n4 = " + n4);    
                }
}