Chapter
2 – Using Methods, Classes, and Objects
Section A - Programming Using Methods
A method is a series of statements that carry out some task.
Example: The first program calls greeting method to perform the greeting task.
public class ch2_1
{
public static void main (String[] args)
{
System.out.println(" use another program");
greeting( );
}
public static void greeting( )
{
System.out.println(" Hi, how are you!");
System.out.println(" My name is Shin Liu");
}
}
Example 2: The SetUpSite class calls the StatementOfPhilosophy to print the philosophy statements
public class SetUpSite
{
public static void main (String[] args)
{
statementOfPhilosophy( );
}
public static void statementOfPhilosophy( )
{
System.out.println(" Event Handlers Incorporated is");
System.out.println(" dedicated to making your event");
System.out.println("a most memorable one.");
}
}
Example 3 : You can call a method from another class.
public class Test
{
public static void main(String[] args)
{
System.out.println
("Calling method from another class:");
SetUpSite.statementOfPhilosophy( );
}
}
Example 1: The demo class calls the prdictRaise class to calculate the new salary.
public class demo
{
public static void main(String[] args)
{
double salary = 200;
System.out.println("Demonstrating some raises");
predictRaise(400);
predictRaise(salary);
}
public static void predictRaise(double money)
{
double newAmount;
newAmount = money * 1.10;
System.out.println("With raise salary is " + newAmount);
}
}
Example 2 : The testdemo class calls the predictRaise method in the demo class.
public class testdemo
{
public static void main(String[] args)
{
double salary= 300;
System.out.println("call the predit method from demo class");
demo.predictRaise(salary);
}
}
Example 1: demo1 class calles the predictRaise method , and passes two arguments to the method.
public class demo1
{
public static void main(String[] args)
{
double salary = 200;
double rate = .15;
System.out.println("Demonstrating some raises");
predictRaise(400, rate);
predictRaise(salary,rate);
}
public static void predictRaise(double money, double rate)
{
double newAmount;
newAmount = money * rate;
System.out.println("With raise salary is " + newAmount);
}
}
Example 2: The testdemo1 class calls the preditRaise method , that is in the demo class
public class testdemo1
{
public static void main(String[] args)
{
double salary= 300;
double rate = .20;
System.out.println("call the predit method from demo class");
demo1.predictRaise(salary,rate);
}
}
Example 1 : The demo2 class calles passes two arguments to predictRaise method and receives a number from the method.
public class demo2
{
public static void main(String[] args)
{
double salary = 200;
double rate = .15;
double newSalary;
System.out.println("Demonstrating some raises");
newSalary = predictRaise(salary, rate);
System.out.println("The new salary is " + newSalary);
}
public static double predictRaise(double money, double rate)
{
double newAmount;
newAmount = money *( 1 + rate);
return newAmount;
}
}
1. Use a method to get values from the user.
Example 1: The fraction class is the blue print.
public class fraction
{
private int numerator;
private int denominator;
public int getnum( )
{
return numerator;
}
public void setnumber(int n, int d)
{
numerator = n;
denominator = d;
}
public int getden()
{
return denominator;
}
public void print( )
{
System.out.println("the fraction is " + numerator + " / " + denominator);
}
public static void main(String[] args)
{
fraction f1= new fraction();
f1.setnumber( 3,8);
f1.print( );
}
}
Example 2 : You can instantiate an object that belongs to another class
public class fraction
{
private int numerator;
private int denominator;
public int getnum( )
{
return numerator;
}
public void setnumber(int n, int d)
{
numerator = n;
denominator = d;
}
public int getden()
{
return denominator;
}
public void print( )
{
System.out.println("the fraction is " + numerator + " / " + denominator);
}
--- In another class ----
public class testfra
{
public static void main(String[] args)
{
fraction f1 = new fraction();
f1.setnumber( 3,8);
f1.print( );
}
}
2. Using constructors to get values from the users.
Example 1: The fraction1 class uses two constructors,- a default constructor and another constructor that assigns two values.
public class fraction1
{
private int numerator;
private int denominator;
fraction1( )
{
numerator = 1;
denominator = 1;
}
fraction1(int n, int d)
{
numerator = n;
denominator = d;
}
public void print( )
{
System.out.println("the fraction is " + numerator + " / " + denominator);
}
}
--- in another class -----
public class testfra1
{
public static void main(String[] args)
{
fraction1 f2 = new fraction1( );
fraction1 f3 = new fraction1( 2,3);
f2.print();
f3.print();
}
}