Revision of introduction in java programming.pptx

Programming with java
Lecture 1
Revision
Structural programming (java)

Constants and Variables
 Named constant
◦ cannot be changed during program execution
◦ declared by using the reserved word final
◦ initialized when it is declared
 Variable (name, value, data type, size)
◦ content may change during program execution
◦ must be declared before it can be used
◦ may not be automatically initialized
◦ if new value is assigned, old one is destroyed
◦ value can only be changed by an assignment statement
or an input (read) statement

Data Types
 Data type: set of values together with a set of operations

Primitive Data Types
 Floating-Point Data Types
◦ Float: precision = 6 or 7
◦ Double: precision = 15
 Boolean: two values
◦ True
◦ False

Values and Memory Allocation
for Integral Data Types

Arithmetic Operators and Operator
Precedence
 Five Arithmetic Operators
◦ + addition
◦ - subtraction
◦ * multiplication
◦ / division
◦ % mod (modulus) operator (integer operands only)
 Unary operator: operator that has one operand
 Binary operator: operator that has two operands

Order of Precedence
1. * / % (same precedence)
2. + - (same precedence)
 Operators in 1 have a higher precedence
than operators in 2.
 When operators have the same level of
precedence, operations are performed from left
to right

Expressions
 Integral expressions
 Floating-point or decimal expressions
 Mixed expressions

Integral Expressions
 All operands are integers
 Examples:
2 + 3 * 5
3 + x – y/7
x + 2 * (y – z) + 18

Floating-point Expressions
 All operands are floating-point numbers
 Examples:
12.8 * 17.5 – 34.50
x * 10.5 + y - 16.2

Mixed Expressions
 Operands of different types
 Examples:
2 + 3.5
6/4 + 3.9
 Integer operands yield an integer result; floatingpoint
numbers yield floating-point results
 If both types of operands are present, the result is
a floating-point number
 Precedence rules are followed

Operators and expressions
 An operator specifies an operation for the JVM to
carry out, E.g., x + y means:
get the value of x,
get the value of y,
add the two values;
 In this example, x and y are the operands
 An expression is a series of operations specified using
constants, variables and operators. E.g.,
x + y, count + 1, a - b - c, a * (b - c)
 The value of an expression is the resulting value after
evaluation

Type conversions (casting)
In general, the assignment statement
<variable> = < expression>;
asks the JVM to evaluate the <expression> and stores the
result in the cells represented by the <variable> .
If the type of the result is different from that of the variable,
a type conversion (casting) is conducted. E.g.,
int x;
double y;
y = 7 / 3; //from int to double, casting is automatic
x = 7.0 / 3; //from double to int, explicit casting is needed
x = (int) (7.0 / 3); //Alright. (int) specifies the casting
// operation that changes the result from double to int

Type Conversion (Casting)
 Used to avoid implicit type coercion
Syntax
(dataTypeName) expression
 Expression evaluated first, then type
converted to dataTypeName
 Examples:
(int)(7.9 + 6.7) = 14
(int)(7.9) + (int)(6.7) = 13

Assignment Statements
x = 1; // Assign 1 to x;
radius = 1.0; // Assign 1.0 to radius;
a = 'A'; // Assign 'A' to a;

Declaring and Initializing
in One Step
 int x = 1;
 double d = 1.4;
 float f = 1.4;

Constants
final datatype CONSTANTNAME = VALUE;
final double PI = 3.14159;
final int SIZE = 3;

Flow of control
( control structure)

(if/if – else) statements
 Examples:
boolean move = false;
if (move)
System.out.println ("I am selling my house.");
else
System.out.println ("I am staying.");
if (name == "fred") {
x = 4;
}
else {
x = 20;
}
NOTE: When the conditional if statement is used only to make an assignment to
one variable:
x = (name == "fred") ? 4 : 20;

Switch-case
 Example:
int day; // Assume this was initialized somewhere.
boolean exerciseDay = false;
boolean weekend = false;
switch (day) {
case 1: // Monday
System.out.println("Monday ... Arr ...sucks");
break;
case 2: // Tuesday
exerciseDay = true;
break;
case 4: // Thursday
exerciseDay = true;
break;
case 0: // Sunday
break;
case 6: // Saturday
weekend = true;
break;
default: // Everything else.
System.out.println ("Ordinary work day.");
break;
}

While loops
 Examples:
int i = 0;
while ((i * i) != 81)
++i;
System.out.println ("The square root of 81 is: " +i);
int j = 0;
while (j < 10) {
System.out.println ("j = " + j); ++j;
}

Continue statements
int x = 0;
while (x < 10) {
x++;
System.out.println(x);
continue;
// you will never get to this point!!
};

Break statements
int x = 0;
while (x < 10) {
x++;
System.out.println(x);
break;
// you will never get to this point!
};

Do-while loops
 Examples:
char ch = 'z';
do {
System.out.print (ch);
--ch;
} while (ch != 'a');
// Loop doing the same thing
while (ch != 'a') {
System.out.print (ch);
--ch;
}

For loops
 Examples:
int sum = 0;
for (int i = 1; i <= 100; ++i)
sum += i;
int loops = 0;
for (int j = 1000; j > 0; j /= 2) {
System.out.println ("j = " + j);
++loops;
}
System.out.println ("It took " + loops + " loops.");

Methods
 Also called “functions"
 Declared with:
◦ A return type (void if no return)
◦ A name
◦ 0 or more parameters
 May be called within any expression
 May be "overloaded" - i.e., multiple functions
may have the same name, as long as they
take different combinations of parameters

Methods
 A Method is a small program that is invoked to
accomplish a task. E.g., b = Math.cos(1.0);
 Math is a built-in class that has many methods. cos() is a
method in Math.
 When the above statement is executed, the method is invoked
and x matches with 1.0. The method computes cos(1.0) and
returns the result, 0.999847. The result is assigned to b.
 Other methods in Math are sin(x), tan(x), sqrt(x), …

Overloaded methods and coercion of
arguments
 A method may have 0, 1, or more parameters. Eg,
public static double random()
 Some of methods are Overloaded methods, which means
that more than one method exists with the same name, but
with different type of parameters.
 Java automatically converts arguments of an incorrect type
into arguments of the type required by the method.
 This process is known as the coercion of arguments

Normal Function
// This function adds all numbers from 1 // to the argument and
returns the sum.
int computeSum (int arg) {
int sum = 0;
for (int i = 1; i <= arg; ++i)
sum += i;
return sum;
}
// This function prints out all of the sums for //each odd number
from 1 to 19.
void functionB () {
for (int i = 1; i <= 19; i += 2)
System.out.println ("computeSum(i)=" + computeSum (i));
}

Main method
 Special function where applications are first
called
 Command line arguments are available as an
array of Strings
 Always declared as "public static void"
 Example:
public static void main (String[] args) {
// Print out the hello world
System.out.println("Testing - Hello World");
}

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