Chapter 4

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Chapter 4

Defining Classes I

This activity contains 15 questions.

Any method can be used as a void method,

so long as the method returns a numeric (not a String) valueso long as the method doesn't accept any argumentswithout any restrictionsso long as the method already is declared to be void

Consider the following statements:

The attributes that describe an object define the objects state of being.
All objects have a state and a set of behaviors.
An object is defined by a class.
A class by itself is not an object.

Which of these four statements are true?

All but (a).All but (c).Only (b) and (c).All four statements are true.

How are local variables are initialized?

Locals are NOT initializedLocals are initialized when they are declared, even if you don't provide an explicit initialization valueLocals are initialized to zeroLocal variables and instance variables both are initialized automatically

In order to distinguish among overloaded methods, the compiler uses the method's signature. A signature is composed of:

A method's name, and the order and types of its parameters.The number, order, types of the method's parameters.A method's name, and the number, order, types of its parameters.A method's name, its return type, and the number, order, and types of its parameters.

The this keyword:

refers to the object of the current classis an argument in a methodmay be used to access non-local variablesonly can be used in an expression on the right side of an assignment statement

What are the purposes of accessor and mutator methods?

Accessors return the value of public instance variables; mutators change the value of public instance variablesMutators return the value of private instance variables; accessors change the value of private instance variablesAccessors return the value of private instance variables; mutators change the value of private instance variablesAccessors and mutators are used with non-void methods to return the value of the method

What is printed by this program?

public class Tiny {

	int num = 1;

	Tiny() {
		System.out.println("constructor");
		++num;
	}

	void increment() {
		System.out.println("increment");
		while (num < 30)
			num += 10;
	}

	void display() {
		System.out.println("num= " + num);
	}

	public static void main(String[] args) {
		Tiny tiny = new Tiny();
		tiny.increment();
		tiny.display();
		System.out.println();
	}
}

constructor
increment
num= 31
increment
num= 1
constructor
increment
num= 22
constructor
increment
num= 32

What is printed?

public class Arith {

	float a = 3, b = 5, c = 7;

	float value(float a, float b, float c) {
		float d = a + b + 2;
		float e = 3 + b + c;
		return (d * e) / 10.0F;
	}

	Arith() {
		float ans = value(a, b, c);
		System.out.println("ans = " + ans);
	}
		

	public static void main(String[] args) {
		new Arith();
	}
}

ans = 15.0ans = 15ans = 2.5ans = 150.0

What is printed?

public class Arith {

	int a = 3, b = 5, c = 7;

	int sum(int a, int b, int c) {
		return (a + b + c);
	}

	Arith() {
		int ans = sum(c, a+b, b);
		System.out.println("ans = " + ans);
	}
		

	public static void main(String[] args) {
		new Arith();
	}
}

ans = 0ans = 15ans = 280ans = 20

What is printed?

public class Arith {

	int fcn(int a, int b) {
		return (a * b);
	}

	double fcn(double a, double b) {
		return (b + a);
	}

	Arith() {
		double dA = fcn(4.5, 5.5);
		double dB = fcn(5, 6);
		System.out.println(dB + " " + dA);
	}

	public static void main(String[] args) {
		new Arith();
	}
}

11.0 10.030.0 10.030.0 24.7510.0 30.0

What is printed?

public class Arith {

	int fcn(int a, int b) {
		return (a * b);
	}

	int fcn(int a, double b) {
		return (int) (a / b);
	}

	Arith() {
		int ans = fcn(fcn(3, 4), 2.0);
		System.out.println("ans = " + ans);
	}

	public static void main(String[] args) {
		new Arith();
	}
}

ans = 6.0ans = 6ans = 24ans = 0

What is printed?

public class Arith {

	int fcn(int a, int b) {
		return (a * b);
	}

	int fcn(int a, double b) {
		return (int) (a / b);
	}

	public static void main(String[] args) {
		Arith arith = new Arith();
		int vA = arith.fcn(7, 
						   arith.fcn(3, 2));
		int vB = arith.fcn(13, 2.0);
		System.out.println(vA + " " + vB);
	}
}

42 2642 67 67 26

What is printed?

public class Arith {

	int fcn(int a, int b) {
		return (a > b) ? a : b;
	}

	public static void main(String[] args) {
		Arith arith = new Arith();
		int num, ans = 0;
		for (num = 0; num < 10; num += 2)
			ans = arith.fcn(ans, num);

		System.out.println("ans = " + ans);
	}
}

ans = 8ans = 9ans = 0ans = 10

What is printed?

public class Even {

	Even() {
		number = 0;
	}

	Even(final int num) {
		number = 2 * num;
	}

	Even prod(Even evB) {
		return 
			new Even((number*evB.number)/4);
	}

	public String toString() {
		return "" + number;
	}

	public static void main(String[] args) {
		Even evA = new Even(3);
		Even evB = new Even(7);
		Even evC = evA.prod(evB);
		System.out.println("evC = " + evC);
	}

	private int number;
}

evC = 10evC = 21evC = 42evC = 84

Which statement(s) is (are) true?

Java programs can have both local and global variables
Java programs can have local variables, but global variables are not part of the language
Java programs can have global variables, but local variables are not part of the language
Java programs can have both local and global variables, so long as their names are spelled differently

All four statements are trueStatements (a) and (d) are trueNone of the statements is trueOnly statement (b) is true

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Chapter 4

Any method can be used as a void method,

How are local variables are initialized?

In order to distinguish among overloaded methods, the compiler uses the method's signature. A signature is composed of:

The this keyword:

What are the purposes of accessor and mutator methods?

What is printed? public class Arith { int a = 3, b = 5, c = 7; int sum(int a, int b, int c) { return (a + b + c); } Arith() { int ans = sum(c, a+b, b); System.out.println("ans = " + ans); } public static void main(String[] args) { new Arith(); } }

What is printed?
public class Arith { int a = 3, b = 5, c = 7; int sum(int a, int b, int c) { return (a + b + c); } Arith() { int ans = sum(c, a+b, b); System.out.println("ans = " + ans); } public static void main(String[] args) { new Arith(); } }