6 1 Explain how an instance method differs from a class method (stat

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6.1 Explain how an instance method differs from a class

method (static method).

6.2 Explain what happens if we write a class named C but

do not implement any constructors in C.

6.3 (a) In a static method, it is easy to differentiate

between calls to instance methods and calls to static

methods. How do you tell them apart? (b) Why is it not as

easy for methods that are called from an instance method?

6.4 Explain what happens when this application runs and

why.

public class C { private int x; private String s; public static

void main(String[] pArgs) { new C(); }

public C() { x = s.length();

System.out.println(\"x = \" + x); } }

6.5 Write the declaration for a class named C that

declares:

(1) a private int instance variable named mX;

(2) a private int class variable named mY initialized to 0;

(3) a private int class constant named A which is

equivalent to 100;

(4) a public int class constant named B which is equivalent

to 200;

(5) public accessor and mutator methods for mX named

getX() and setX();

(6) public accessor and mutator methods for mY named

getY() and setY();

(7) a constructor that has one int input parameter named

pX which calls setX() to initialize mX to pX;

(8) a default constructor that calls C(int) to initialize mX to

-1.

6.6 Continuing with the previous exercise, write the

declaration for a class named Main that implements the

main() method. Within main() suppose we wish to

instantiate a C object named cObj1 calling the default

constructor. Write the code to do this.

6.7 Continuing, write the code to instantiate another C

object named cObj2 calling the second constructor to

initialize the mX instance variable to 10.

6.8 Continuing, within main(), are the following statements

legal, i.e., do they compile? If so, explain what happens

when the statement is executed. If not, explain why the

statement is illegal.

(a) int a1 = C.mX;

(b) int a2 = C.mY;

(d) int a4 = C.B;

(e) cObj1.C(20);

(f) int a5 = cObj1.getX();

(g) cObj1.setX(20);

(h) cObj2.setX(cObj1.getX());

(i) int a6 = C.getX();

(j) C.setX(20);

(k) int a7 = cObj1.getY();

(l) cObj1.setY(20);

(m) int a8 = C.getY();

(n) C.setY(20);

6.9 Continuing, suppose we add these two methods to the

declaration of class C. For each assignment statement, if it

is legal (compiles) explain what happens when the

statement is executed. For each assignment statement that

is illegal (syntax error) explain why the code is illegal.

public void f() { mX = 0; mY = 0; } public static void g() {

mX = 0; mY = 0; }

Solution

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6.1 Explain how an instance method differs from a class method (static method). 6.2 Explain what happens if we write a class named C but do not implement any constructors in C. 6.3 (a) In a static method, it is easy to differentiate between calls to instance methods and calls to static methods. How do you tell them apart? (b) Why is it not as easy for methods that are called from an instance method? 6.4 Explain what happens when this application runs and why. public class C { private int x; private St ring s; public static void main(String[] pArgs) { new C(); } public C() { x = s.length(); System.out.println(\"x = \" + x); } } 6.5 Write the declaration for a class named C that declares: (1) a private int instance variable named mX; (2) a private int class variable named mY initialized to 0; (3) a private int class constant named A which is equivalent to 100; (4) a public int class constant named B which is equivalent to 200; (5) public accessor and mutator methods for mX named getX() and setX(); (6) public accessor and mutator methods for mY named getY() and setY(); (7) a constructor that has one int input parameter named pX which calls setX() to initialize mX to pX; (8) a default constructor that calls C(int) to initialize mX to -1. 6.6 Continuing with the previous exercise, write the declaration for a class named Main that implements the main() method. Within main() suppose we wish to instantiate a C object named cObj1 calling the default constructor. Write the code to do t ...
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