|
|
examples -run these
ex1
public class HelloWorld {
// A program to display the message
// "Hello World!" on standard output
public static void main(String[] args) {
System.out.println("Hello World!");
}
} // end of class HelloWorld
ex 2
public class Interest {
/*
This class implements a simple program that
will compute the amount of interest that is
earned on $17,000 invested at an interest
rate of 0.07 for one year. The interest and
the value of the investment after one year are
printed to standard output.
*/
public static void main(String[] args) {
/* Declare the variables. */
double principal; // The value of the investment.
double rate; // The annual interest rate.
double interest; // Interest earned in one year.
/* Do the computations. */
principal = 17000;
rate = 0.07;
interest = principal * rate; // Compute the interest.
principal = principal + interest;
// Compute value of investment after one year, with interest.
// (Note: The new value replaces the old value of principal.)
/* Output the results. */
System.out.print("The interest earned is $");
System.out.println(interest);
System.out.print("The value of the investment after one year is $");
System.out.println(principal);
} // end of main()
} // end of class Interest
ex 3
public class TimedComputation {
/* This program performs some mathematical computations and displays
the results. It then reports the number of seconds that the
computer spent on this task.
*/
public static void main(String[] args) {
long startTime; // Starting time of program, in milliseconds.
long endTime; // Time when computations are done, in milliseconds.
double time; // Time difference, in seconds.
startTime = System.currentTimeMillis();
double width, height, hypotenuse; // sides of a triangle
width = 42.0;
height = 17.0;
hypotenuse = Math.sqrt( width*width + height*height );
System.out.print("A triangle with sides 42 and 17 has hypotenuse ");
System.out.println(hypotenuse);
System.out.println("\nMathematically, sin(x)*sin(x) + "
+ "cos(x)*cos(x) - 1 should be 0.");
System.out.println("Let's check this for x = 1:");
System.out.print(" sin(1)*sin(1) + cos(1)*cos(1) - 1 is ");
System.out.println( Math.sin(1)*Math.sin(1)
+ Math.cos(1)*Math.cos(1) - 1 );
System.out.println("(There can be round-off errors when "
+ " computing with real numbers!)");
System.out.print("\nHere is a random number: ");
System.out.println( Math.random() );
endTime = System.currentTimeMillis();
time = (endTime - startTime) / 1000.0;
System.out.print("\nRun time in seconds was: ");
System.out.println(time);
} // end main()
} // end class TimedComputation