Notes

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41. What is the output of the following program?

import java.util.Date;

public class Test {
public static void main(String[] args) {
Date date = new Date(1234567);
m1(date);
System.out.print(date.getTime() + " ");

m2(date);
System.out.println(date.getTime());
}

public static void m1(Date date) {
date = new Date(7654321);
}

public static void m2(Date date) {
date.setTime(7654321);
}
}
a. 1234567 1234567
b. 1234567 7654321
c. 7654321 1234567
d. 7654321 7654321
Key:b

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Section 9.11 Array of Objects
42. Given the declaration Circle[] x = new Circle[10], which of the following statement is most accurate?
a. x contains an array of ten int values.
b. x contains an array of ten objects of the Circle type.
c. x contains a reference to an array and each element in the array can hold a reference to a Circle object.
d. x contains a reference to an array and each element in the array can hold a Circle object.
Key:c

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43. Assume java.util.Date[] dates = new java.util.Date[10], which of the following statements are true?
a. dates is null.
b. dates[0] is null.
c. dates = new java.util.Date[5] is fine, which assigns a new array to dates.
d. dates = new Date() is fine, which creates a new Date object and assigns to dates.
Key:bc

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Section 9.12 Immutable Objects and Classes
44. Which of the following statements are true about an immutable object?
a. The contents of an immutable object cannot be modified.
b. All properties of an immutable object must be private.
c. All properties of an immutable object must be of primitive types.
d. An object type property in an immutable object must also be immutable.
e. An immutable object contains no mutator methods.
Key:abde

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Section 9.13 Scope of Variables
45. What is the output for the first statement in the main method?
public class Foo {
static int i = 0;
static int j = 0;

public static void main(String[] args) {
int i = 2;
int k = 3;
{
int j = 3;
System.out.println("i + j is " + i + j);
}

k = i + j;
System.out.println("k is " + k);
System.out.println("j is " + j);
}
}
a. i + j is 5
b. i + j is 6
c. i + j is 22
d. i + j is 23
Key:d The first + operator in the expression "i + j is " + i + j is evaluated.

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46. What is the output for the second statement in the main method?
public class Foo {
static int i = 0;
static int j = 0;

public static void main(String[] args) {
int i = 2;
int k = 3;
{
int j = 3;
System.out.println("i + j is " + i + j);
}

k = i + j;
System.out.println("k is " + k);
System.out.println("j is " + j);
}
}
a. k is 0
b. k is 1
c. k is 2
d. k is 3
Key:c When computing k = i + j, i is 2 and j is 0.

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47. What is the output for the third statement in the main method?
public class Foo {
static int i = 0;
static int j = 0;

public static void main(String[] args) {
int i = 2;
int k = 3;
{
int j = 3;
System.out.println("i + j is " + i + j);
}

k = i + j;
System.out.println("k is " + k);
System.out.println("j is " + j);
}
}
a. j is 0
b. j is 1
c. j is 2
d. j is 3
Key:a

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48. You can declare two variables with the same name in __________.
a. a method one as a formal parameter and the other as a local variable
b. a block
c. two nested blocks in a method (two nested blocks means one being inside the other)
d. different methods in a class
Key:d

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Section 9.14 The this Keyword
49. Analyze the following code:

class Circle {
private double radius;

public Circle(double radius) {
radius = radius;
}
}
a. The program has a compile error because it does not have a main method.
b. The program will compile, but you cannot create an object of Circle with a specified radius. The object will always have radius 0.
c. The program has a compile error because you cannot assign radius to radius.
d. The program does not compile because Circle does not have a default constructor.
Key:b You have replace radius = radius by this.radius = radius

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50. Analyze the following code:

class Test {
private double i;

public Test(double i) {
this.t();
this.i = i;
}

public Test() {
System.out.println("Default constructor");
this(1);
}

public void t() {
System.out.println("Invoking t");
}
}
a. this.t() may be replaced by t().
b. this.i may be replaced by i.
c. this(1) must be called before System.out.println("Default constructor").
d. this(1) must be replaced by this(1.0).
Key:ac

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51. Which of the following can be placed in the blank line in the following code?
public class Test {
private int id;

public void m1() {
_____.id = 45;
}
}

a. this
b. Test
Key:a