Basic Programming using Java

   
 Variables and Data types          

Although you can create a complete database without writing code, in some cases, some tasks cannot be performed automatically. For these tasks, you must temporarily use values that you can change at will and dismiss when not needed anymore.           A variable is a value that you "put" into the computer memory when necessary. The value is lost when the application closes. To proceed, you must communicate to the computer that you will need a portion of its memory to hold a certain value. When you communicate this, the computer reserves the necessary portion for you and makes it available when you need it.             Communicating your intention is also referred to as declaring a variable. Because there can be various values used while the application is running, the computer would need two pieces of information to hold a value: a name that can be used to identify the portion of memory and the amount of memory that will be necessary to store the value.            You often need to store values temporarily when performing calculations with Visual Basic. For example, you might want to calculate several values, compare them, and perform different operations on them, depending on the result of the comparison. You need to retain the values if you want to compare them, but you don't need to store them in a property.         All variables in the Java language must have a data type. The Java language supports a full range of primitive data types, including integer,floating point, character, and boolean. In the example program, count is an integer, as indicated by the int keyword that precedes it.                                        JavaScript If...Else Statements Conditional statement                               In  computer science, conditional statements, conditional expressions and conditional constructs are features of a programming language which perform different computations or actions depending on whether a programmer-specified Boolean condition evaluates to true or false. Apart from the case of branch prediction,  this is always achieved by selectively altering the control flow based on some condition.              In imperative programming languages, the term "conditional statement" is usually used, whereas in functional programming, the terms "conditional expression" or "conditional construct" are preferred, because these terms all have distinct meanings. IF-statements                     Before discussing the actual structure of the if statement, let us examine the meaning of TRUE and FALSE in computer terminology. A true statement is one that evaluates to a nonzero number. A false statement evaluates to zero.

             For example, the check 0 == 2 evaluates to 0. The check 2 == 2 evaluates to a 1. If this confuses you, try to use a cout statement to output the result of those various comparisons (for example cout<< ( 2 == 1 );)

Example
Make a "Good day" greeting if the hour is less than 18:00:
if (hour < 18) {
greeting = "Good day";
}

The else Statement

          Use the else statement to specify a block of code to be executed if the condition is false.
if (condition) {
block of code to be executed if the condition is true
} else {
block of code to be executed if the condition is false
}
Example
       If the hour is less than 18, create a "Good day" greeting, otherwise "Good evening":
if (hour < 18) {
greeting = "Good day";
} else {
greeting = "Good evening";
}

The else if Statement    

              Use the else if statement to specify a new condition if the first condition is false.
Syntax
if (condition1) {
block of code to be executed if condition1 is true
} else if (condition2) {
block of code to be executed if the condition1 is false and condition2 is true
} else {
block of code to be executed if the condition1 is false and condition2 is false
}
Example
        If time is less than 10:00, create a "Good morning" greeting, if not, but time is less than 20:00, create a "Good day" greeting, otherwise a "Good evening":
if (time < 10) {
greeting = "Good morning";
} else if (time < 20) {
greeting = "Good day";
} else {
greeting = "Good evening";
}

The if-then Statement         

          The if-then statement is the most basic of all the control flow statements. It tells your program to execute a certain section of code only if a particular test evaluates to true. For example, the Bicycle class could allow the brakes to decrease the bicycle's speed only if the bicycle is already in motion. One possible implementation of the applyBrakes method could be as follows:
void applyBrakes() { // the "if" clause: bicycle must be moving if (isMoving){ // the "then" clause: decrease current speed currentSpeed--; } }
            If this test evaluates to false (meaning that the bicycle is not in motion), control jumps to the end of the if-then statement.
           In addition, the opening and closing braces are optional, provided that the "then" clause contains only one statement:
void applyBrakes() { // same as above, but without braces if (isMoving) currentSpeed--; }

The if-then-else Statement   
             The if-then-else statement provides a secondary path of execution when an "if" clause evaluates to false. You could use an if-then-else statement in the applyBrakes method to take some action if the brakes are applied when the bicycle is not in motion. In this case, the action is to simply print an error message stating that the bicycle has already stopped.
void applyBrakes() { if (isMoving) { currentSpeed--; } else { System.err.println("The bicycle has already stopped!"); } }
                  The following program, if,else, assigns a grade based on the value of a test score: an A for a score of 90% or above, a B for a score of 80% or above, and so on.
class IfElseDemo {

 public static void main(String[] args) {

 int testscore = 76;

 char grade;

 if (testscore >= 90) { 

      grade = 'A'; 

 } else if (testscore >= 80) { 

      grade = 'B';

 } else if (testscore >= 70) {

      grade = 'C';

 } else if (testscore >= 60) {

      grade = 'D' 

 } else { grade = 'F';

 } 

 System.out.println("Grade = " + grade);

     

      }

 }

Looping statements
      Types of Loops. While a given expression is true it repeats the statement in the loop body. Before executing the loop body it tests the condition for true or false. It is like a while loop but it tests the condition after executing the loop body.

DATA TYPES
         In computer science and computer programming, a data type or simply type is a classification identifying one of various types of data, such as real, integer or Boolean, that determines the possible values for that type; the operations that can be done on values of that type; the meaning of the data; and the way values ...

                                          Java types

INTEGERS TYPE

byte:The byte data type is an 8-bit signed two's complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive). The byte data type can be useful for saving memory in large arrays, where the memory savings actually matters. They can also be used in place of int where their limits help to clarify your code; the fact that a variable's range is limited can serve as a form of documentation.
short: The short data type is a 16-bit signed two's complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive). As with byte, the same guidelines apply: you can use a short to save memory in large arrays, in situations where the memory savings actually matters.
int: By default, the int data type is a 32-bit signed two's complement integer, which has a minimum value of -231 and a maximum value of 231-1. In Java SE 8 and later, you can use the int data type to represent an unsigned 32-bit integer, which has a minimum value of 0 and a maximum value of 232-1. Use the Integer class to use int data type as an unsigned integer. See the section The Number Classes for more information. Static methods like compare Unsigned, divide Unsigned etc have been added to the integer class to support the arithmetic operations for unsigned integers.
long: The long data type is a 64-bit two's complement integer. The signed long has a minimum value of -263 and a maximum value of 263-1. In Java SE 8 and later, you can use thelong data type to represent an unsigned 64-bit long, which has a minimum value of 0 and a maximum value of 264-1. Use this data type when you need a range of values wider than those provided by int. The long class also contains methods like compare Unsigned, divide Unsigned etc to support arithmetic operations for unsigned long.
        Each types has a maximum value, based on their binary representation:

–Bytes: 8-bits, ± 128
–Short: 16-bits, ± 215 ≈ 32,000
–Int: 32-bits, ± 231 ≈ 2 billion
–Long: 32-bits, ± 263 ≈ really big

FLOATING POINT (Decimal) TYPE

float: The float data type is a single-precision 32-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the floating-points types, format and values section of the Java Language Specification. As with the recommendations for byte and short, use a float (instead of double) if you need to save memory in large arrays of floating point numbers. This data type should never be used for precise values, such as currency. For that, you will need to use the  class instead.number and string covers Big Decimal and other useful classes provided by the Java platform.
double: The double data type is a double-precision 64-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the floating-points, types, format and values section of the Java Language Specification. For decimal values, this data type is generally the default choice. As mentioned above, this data type should never be used for precise values, such as currency.

    OTHER TYPES

Boolean: The Boolean data type has only two possible values: true and false. Use this data type for simple flags that track true/false conditions. This data type represents one bit of information, but its "size" isn't something that's precisely defined.
char: The char data type is a single 16-bit Unicode character. It has a minimum value of '\u0000' (or 0) and a maximum value of 'f' (or 65,535 inclusive).
String:In computer programming, a string is traditionally a sequence of characters, either as a literal constant or as some kind of variable. The latter may allow its elements to be mutated and the length changed, or it may be fixed (after creation).