1. Arrays allow us to store multiple values of the same type in a single variable. We declare an array by specifying its type, name, and size. 2. The Math class contains commonly used mathematical functions like trigonometric, exponent, rounding, and random number generation methods. 3. We can pass arrays to methods in Java. When an array is passed as a parameter, any changes made to the array inside the method will be reflected outside the method.

1. Lecture#6+7

2. Overloading Methods
Example 4.3 Overloading the max Method
public static double max(double num1, double
num2) {
if (num1 > num2)
return num1;
else
return num2;
}

3. Type Casting
 If x is a float and y is an int, what will be the data type of
the following expression?
 x * y
 The answer is float.
 The above expression is called a mixed expression.
 The data types of the operands in mixed expressions are
converted based on the promotion rules. The promotion
rules ensure that the data type of the expression will be the
same as the data type of an operand whose type has the
highest precision.

4. Explicit Type Casting
 Explicit type conversion is a type conversion which is
explicitly defined within a program (instead of being done
by a compiler for implicit type conversion).
 Instead of relying on the promotion rules, we can make an
explicit type cast by prefixing the operand with the data
type using the following syntax:
( <data type> ) <expression>
 Example
(float) x / 3
(int) (x / y * 3.0)
Type case x to float and
then divide it by 3.
Type cast the result of the
expression x / y * 3.0 to
int.

5. Constants
 We can change the value of a variable. If we want the value to remain
the same, we use a constant.
final double PI = 3.14159;
final int MONTH_IN_YEAR = 12;
final short FARADAY_CONSTANT = 23060;
These are constants,
also called named
constant.
The reserved word
final is used to
declare constants.
These are called
literal constant.

6. Sample Code Fragment
//code fragment to input radius and output
//area and circumference
final double PI = 3.14159;
double radius, area, circumference;
//compute area and circumference
area = PI * radius * radius;
circumference = 2.0 * PI * radius;
System.out.println("Given Radius: " + radius);
System.out.println("Area: " + area);
System.out.println(" Circumference: “ + circumference);

7. String Input
 Using a Scanner object is a simple way to input data from the standard input
System.in, which accepts input from the keyboard.
 First we need to associate a Scanner object to System.in as follows:
 After the Scanner object is set up, we can read data.
 The following inputs the first name (String):
import java.util.Scanner;
Scanner scanner;
scanner = new Scanner(System.in);
System.out.print (“Enter your first name: ”);
String firstName = scanner.next();
System.out.println(“Nice to meet you, ” +
firstName + “.”);

8. Numerical Input
 We can use the same Scanner class to input numerical
values
Scanner scanner = new Scanner(System.in);
int age;
System.out.print( “Enter your age: “ );
age = scanner.nextInt();

9. Scanner Methods
Method Example
nextByte( ) byte b = scanner.nextByte( );
nextDouble( ) double d = scanner.nextDouble( );
nextFloat( ) float f = scanner.nextFloat( );
nextInt( ) int i = scanner.nextInt( );
nextLong( ) long l = scanner.nextLong( );
nextShort( ) short s = scanner.nextShort( );
next() String str = scanner.next();

10. The Math class
 The Math class in the java.lang package contains class methods for
commonly used mathematical functions.
 Class methods:
 Trigonometric Methods
 Exponent Methods
 Rounding Methods
 min, max, abs, and random Methods
double num, x, y;
x = …;
y = …;
num = Math.sqrt(Math.max(x, y) + 12.4);

11. Some commonly use Math Class
Methods
Method Description
exp(a) Natural number e raised to the power of a.
log(a) Natural logarithm (base e) of a.
floor(a) The largest whole number less than or
equal to a.
max(a,b) The larger of a and b.
pow(a,b) The number a raised to the power of b.
sqrt(a) The square root of a.
sin(a) The sine of a. (Note: all trigonometric
functions are computed in radians)

12. Trigonometric Methods
 sin(double a)
 cos(double a)
 tan(double a)
 acos(double a)
 asin(double a)
 atan(double a)
Exponent Methods
 exp(double a)
Returns e raised to the power of a.
 log(double a)
Returns the natural logarithm of a.
 pow(double a, double b)
Returns a raised to the power of b.
 sqrt(double a)
Returns the square root of a.

13. Rounding Methods
 double ceil(double x)
x rounded up to its nearest integer. This integer is returned as a double value.
 double floor(double x)
x is rounded down to its nearest integer. This integer is returned as a double value.
 double rint(double x)
x is rounded to its nearest integer. If x is equally close to two integers, the even one
is returned as a double.
 int round(float x)
Return (int)Math.floor(x+0.5).
 long round(double x)
Return (long)Math.floor(x+0.5).
min, max, abs, and random
 max(a, b)and min(a, b)
Returns the maximum or minimum of two parameters.
 abs(a)
Returns the absolute value of the parameter.
 random()
Returns a random double value
in the range [0.0, 1.0).

14. Chapter 5 Arrays
 Introducing Arrays
 Declaring Array Variables, Creating Arrays, and
Initializing Arrays
 Passing Arrays to Methods

15. Introducing Arrays
Array is a data structure that represents a collection of
the same types of data.
myList[0]
myList[1]
myList[2]
myList[3]
myList[4]
myList[5]
myList[6]
myList[7]
myList[8]
myList[9]
double[] myList = new double[10];
myList reference
An Array of 10
Elements
of type double

16. Declaring Array Variables
 datatype[] arrayname;
Example:
double[] myList;
 datatype arrayname[];
Example:
double myList[];

17. Creating Arrays
arrayName = new datatype[arraySize];
Example:
myList = new double[10];
myList[0] references the first element in the array.
myList[9] references the last element in the array.

18. Declaring and Creating
in One Step
 datatype[] arrayname = new
datatype[arraySize];
double[] myList = new double[10];
 datatype arrayname[] = new
datatype[arraySize];
double myList[] = new double[10];

19. The Length of Arrays
Once an array is created, its size is fixed. It
cannot be changed. You can find its size
using
arrayVariable.length
For example,
myList.length returns 10

20. Initializing Arrays
 Using a loop:
for (int i = 0; i < myList.length; i++)
myList[i] = i;
 Declaring, creating, initializing in one step:
double[] myList = {1.9, 2.9, 3.4, 3.5};
This shorthand syntax must be in one statement.

21. Declaring, creating, initializing Using the
Shorthand Notation
double[] myList = {1.9, 2.9, 3.4, 3.5};
This shorthand notation is equivalent to the following
statements:
double[] myList = new double[4];
myList[0] = 1.9;
myList[1] = 2.9;
myList[2] = 3.4;
myList[3] = 3.5;

22. CAUTION
Using the shorthand notation,
you have to declare, create,
and initialize the array all
in one statement. Splitting it
would cause a syntax error.
For example, the following is
wrong:
double[] myList;
myList = {1.9, 2.9, 3.4, 3.5};

23. Passing Arrays to Methods
Java uses pass by value to pass
parameters to a method. There are
important differences between passing
a value of variables of primitive data
types and passing arrays.
 For a parameter of a primitive type
value, the actual value is passed.
Changing the value of the local
parameter inside the method does not
affect the value of the variable
outside the method.
 For a parameter of an array type, the
value of the parameter contains a
reference to an array; this reference
is passed to the method. Any changes
to the array that occur inside the

24. THE END