Chapter 1 Homework Answers

C H A P T E R  1  INTRODUCTION

•• R1.7 What does this program print?

public class Test
{
public static void main(String[] args)
{
System.out.println("39 + 3");
System.out.println(39 + 3);
}
}

Answer : 
The first statement System.out.println("39 + 3");
print "39 + 3" in line and dawn line .

Secend statement System.out.println(39 + 3);
print the sum of two number 42 

•• R1.8 What does this program print? Pay close attention to spaces.
public class Test
{
public static void main(String[] args)
{
System.out.print("Hello");
System.out.println("World");
}

}

Answer : 
print HelloWord in the same line and down line .

•• R1.9 What is the compile-time error in this program?
public class Test
{
public static void main(String[] args)
{
System.out.println("Hello", "World!");
}
}

Answer : 
compile-time error  (syntax error ) is comma between 
 "Hello", "World!" .
to correct it replace comma with + . 

•• R1.13 Write an algorithm to settle the following question: A bank account starts out with
$10,000. Interest is compounded monthly at 6 percent per year (0.5 percent per
month). Every month, $500 is withdrawn to meet college expenses. After how many

years is the account depleted?

Answer : 

Step 1 Determine the inputs and outputs .
The inputs are balance, monthly interest and monthly withdraw.
The outputs the number of years that required for depleted account.

Step 2 Break down the problem into smaller tasks.

For each month, we need to know the balance after increase and decrease monthly, the increase is monthly interest is 0.5 % the decrease monthly withdraw is 500, after how many years and months the account depleted.

Step 3 Describe each subtask in pseudocode. Initial balance = 10000 .
Repeat the following steps:
Balance after each month = ( balance * 1.005 ) – 500 .
If balance < 500

Stop you cannot withdraw.

Step 4 Test pseudocode by working a problem.
Initial balance = 10000 $.
Balance after first month = ( 10000 * 1.005 ) – 500 = 9550 .
Balance after second month = (9550 * 1.005 ) – 500 = 9079.75
Balance after third month = (9097.75 * 1.005 ) – 500 = 8643.23875 .
.
.
.
Balance after twenty-one months =
(559.3980531942129 * 1.005 ) – 500 = 62.19504346018391

The balance will depleted after twenty one month that’s mean after 1.75 years the account depleted.


code : 

public class Balance {

    double balance = 10000;   

    double years;    int months = 0; 

    public void getYears() {   

    for (;balance >= 500;) {    

        balance = balance * 1.005;   

         balance = balance - 500;      

      months++;

       }     

       years = months / 12.0;      

      System.out.println("The balance will depleted after " + months + " month");            System.out.println("that’s mean after " + years + " years the account      depleted.");

           }

}

to test it : 

public class Test
{
public static void main(String[] args){
Balance get = new Balance();
get.getYears();
}

}

run:
The balance will depleted after 21 month

that’s mean after 1.75 years the account depleted.


•• E1.16 Type in and run the following program. Then modify it to print “Hello, name!”,
displaying the name that the user typed in.
import javax.swing.JOptionPane;
public class DialogViewer
{
public static void main(String[] args)
{
String name = JOptionPane.showInputDialog("What is your name?");

System.out.println(name);

End of Answers