A+ Answers

How does a variable of a primitive type differ from a reference variable?

What does the operator new do?

3. Consider the following statements:
String str = "Going to the amusement park";
char ch;
int len;
int position;
a. What value is stored in ch by the following statement? ch = str.charAt(0);

b. What value is stored in ch by the following statement? ch = str.charAt(10);

c. What value is stored in len by the following statement? len = str.length();

d. What value is stored in position by the following statement? position = str.indexOf('t');

e. What value is stored in position by the following statement? position = str.indexOf("park");

5. Which of the following statements are valid? If they are invalid, explain why.

b. System.out.println(cube(num1, num3, num2));

c. System.out.println(cube(6.0, 8.0, 10.5));

d. System.out.println(num1 + " " + num3);

e. System.out.println(cube(num1, num3));

f. value = cube(num1, int2, num3);

g. value = cube(7, 8, 9);

6. Why do users prefer a GUI over a nongraphical user interface?

7. Write necessary statements to create the following GUI components:
a. A JLabel with the text string "Enter the number of courses"

b. A JButton with the text string "Run"

c. The title "Welcome Home!" for an existing window

d. A width of 200 pixels and a height of 400 pixels for an existing window

8. Correct the syntax errors in the following program:
public class RTwo extends JFrame
{
public RTwoProgram()
{
private JLabel length, width, area;
setTitle("Good day Area");
length = JLabel("Enter the length);
width = JLabel("Enter the width);
area = JLabel("Area: ");
containerPane = ContentPane();
pane.setLayout(GridLayout(4,1));
setSize(WIDTH,HEIGHT);
setVisible();
setDefaultCloseOperation(EXIT_ON_CLOSE);
}
public static void main(String args[])
{
RTwoProgram R2 = new RTwoProgram();
}
}

9. What is the output of the following program segments?
a. if (6<2*5)
System.out.print("Hello");
System.out.print(" There");

b. if ('a' > 'b' || 66 > (int)('A'))
System.out.println("#*#");

c. if (7<=7)
System.out.println(6 - 9 * 2 / 6);

d. if { (7<8)
System.out.println("2 4 6 8");
System.out.println("1 3 5 7); }

e. if (5 < 3)
System.out.println("*");

else if
(7 == 8) System.out.println("&");
else
System.out.println("$");

10. Write Java statements that output Democrat if the party affiliation code is 'D', Republican if the party affiliation code is 'R', and other otherwise.

11. Suppose that you have the following declaration:
int j = 0;
The output of the statement

if ((8 > 4) || (j++ == 7)) System.out.println("j = " + j);
is
j=0
while the output of the statement
if ((8 > 4) | (j++ == 7)) System.out.println("j = " + j);
is
j = 1
Explain why.

12. Suppose the input is 5. What is the value of alpha after the following Java code executes? (Assume that alpha is an int variable and console is a Scanner object initialized to the keyboard.)
alpha = console.nextInt();
switch (alpha)
{
case 1:

case 2:
alpha = alpha + 2;
break;

case 4:
alpha++;

case 5:
alpha = 2 * alpha;

case 6: alpha = alpha + 5; break;
default:
alpha--;

}

13. Suppose the input is 6. What is the value of a after the following Java code executes? (Assume that all variables are properly declared.)

a = console.nextInt();

if (a > 0)
switch (a)

{

case 1:
a = a + 3;

case 3:
a++;
break;

case 6:
a = a + 6;

case 8: a
= a * 8;
break;

default:
a--;
}
else
a = a + 2;

14. The following program contains errors. Correct them so that the program runs and outputs w =21.
public class Mystery
{
static final int SECRET = 5;
public static void main(String[] args)
{
int x, y, w, z;
z = 9;

if z > 10
x = 12; y = 5, w = x + y + SECRET;
else
x = 12; y = 4, w = x + y + SECRET;
System.out.println("w = " + w);
}
}

16. Name two GUI input components.