Review Exercise

Part 1: ArrayList

n Assume that variable myList is an ArrayList containing at least two objects.

Which of the following code segments moves the first object in the list to the end of the list?

A. myList.add(myList.get(0));

B. myList.add(myList.remove(0)); ANSWER

C. myList.add(0, myList.remove(0));

D. myList.add(myList.size(), myList.get(0));

E. myList.add(myList.remove(myList.size()-1));

n Consider the following code segment:

ArrayList<Integer> L = new ArrayList<Integer();

for(int k = 0; k<9; k++)

{

L.add(new Integer(k))

}

for (int k = 0; k<5; k++)

{

Object tmp = L.get(k);

L.set(k, L.get(8-k));

L.set(8-k, tmp);

}

for (int k = 0; k<9; k++)

{

System.out.print (L.get(k) + " ");

}

What is printed when this code executes?

A. 0 1 2 3 4 5 6 7 8

B. 8 7 6 5 4 3 2 1 0 ANSWER

C. 0 1 2 2 4 3 2 1 0

D. 0 0 0 0 0 0 0 0 0

E. 8 8 8 8 8 8 8 8 8

n Assume that variable L is an ArrayList and that the method call L.size() returns 10. Which of the following method calls does not cause a run time error?

A. L.add(10, "hello"); ANSWER

B. L.add(20, "hello");

C. L.get(10);

D. L.set(10, "hello");

E. L.remove(10);

n Consider the following code. Note that this uses a "plain" ArrayList instead of specifying the type of items that will be stored in the list.

ArrayList L = New ArrayList();

L.add("one");

L.add("two");

L.add("three);

System.out.println((Integer) L.get(L.size()-1));

Which of the following statements about this code is true?

A. The code will not compile because the last line casts the result of the call to get to an Integer, but the values stored in the list are of type String.

B. The code will compile but there will be a runtime error because the last line casts the result of the call to get to an Integer, but the values stored in the list are of type

String. ANSWER

C. The code will compile but there will be a runtime error because the last line calls get with a value that is too large.

D. The code will compile and run without error and will print 3.

E. The code will compile and print without error and will print three.

n Assume that the type of variable strList is ArrayList<String>. Consider the following two code segments, both of which are intended to add an exclamation point to the end of each

string in the list.

Segment 1

for (int k = 0, k<strList.size(); k++)

{

Str tmp = strList.remove(k);

strList.add(k, tmp + "!");

}

Segment 2

for (int k = 0; k<strList.size(); k++)

{

String tmp = strList.get(k);

strList.set(k, tmp + "!");

}

Which of the following statements about these two code segments is true?

A. Both will work as intended, and they will be equally efficient.

B. Both will work as intended; Segment 1 will be more efficient than Segment 2.

C. Both will work as intended; Segment 2 will be more efficient than segment 1. ANSWER

D. Only Segment 1 will work as intended.

E. Only Segment 2 will work as intended.

n Which of the following declarations will cause an error?

I. ArrayList<String> stringList = new ArrayList<String>();

II. ArrayList<int> intList = new ArrayList<int>();

III. ArrayList<Comparable> compList = new ArrayList<Comparable>();

A. I only

B. II only ANSWER

C. III only

D. I and III only

E. II and III only

n Consider these declarations

ArrayList<String> stringList = new ArrayList<String>();

String ch = " ";

Integer intOb = new Integer(5);

Which statement will cause an error?

A. strList.add(ch);

B. strList.add(new String("handy andy"));

C. strList.add(intOb.toString());

D. strList.add(ch + 8);

E. strList.add(intOb + 8); ANSWER

n Let list be an ArrayList<Integer> containing these elements

2 5 7 6 0 1

Which of the following statements would not cause an error to occur? Assume that each statement applies to the given list, independent of other statements.

A. Object ob = list.get(6);

B. Integer intOb = list.add(3,4);

C. list.add(6,9); ANSWER

D. Object x = list.remove(6);

E. Object y = list.set(6,8);

Part 2: One-D Arrays

n Consider the following code segment. The line numbers are included for reference.

1	Int [ ] A = new int[3];
2	Int [ ] B = new int[10];
3	B[9] = 30;
4	A = B;
5	A[9] = 20;
6	B[9] = 10;
7	System.out.println(A[9]);

What happens when this code is compiled and executed?

A. Line 5 will cause a compile-time error because of an out-of-bounds array index.

B. Line 5 will cause a runtime error because of an out-of-bounds array index.

C. The code will compile and execute without error. The output will be 10. ANSWER

D. The code will compile and execute without error. The output will be 20.

E. The code will compile and execute without error. The output will be 30.

n Which of the following statements is not true?

A. Every object has an equals method.

B. If a programmer does not write an equals method for a new class, the default method will return true if an only if all fields of the two instances of the class contain the

same values. ANSWER

C. The equals method for Strings returns true if and only if the two Strings contain the same sequence of characters.

D. The equals method for arrays returns true if and only if the two arrays point to the same chunk of memory.

E. The equals method for Strings will return false if one String is shorter than the other.

n Consider the following code segment:

String s1 = "abc";

String s2 = s1;

String s3 = s2;

After this code executes, which of the following expressions would evaluate to true?

I. s1.equals(s3)

II. s1 == s2

III. s1 == s3

A. I only

B. II only

C. III only

D. I and II only

E. I, II, and III ANSWER

n Consider the following code segment:

int [ ] A = {1, 2, 3};

int [ ] B = {1, 2, 3};

int [ ] C = A;

After this code executes, which of the following expressions would evaluate to true?

I. A.equals(B)

II. A == B

III. A == C

A. I only

B. II only

C. III only ANSWER

D. I and III only

E. I, II, and III

n Which of the following correctly initializes an array arr to contain four elements each with value 0?

I. int [ ] arr = {0, 0, 0, 0};

II. int [ ] arr = new int[4];

III. int[ ] arr = new int[4];

for(int i = 0; i<arr.length; i++)

arr[i] = 0;

A. I only

B. III only

C. I and III only

D. II and III only

E. I, II, and III ANSWER

n The following program segment is intended to find the index of the first negative integer in arr[0]...arr[N-1], where arr is an array of N integers.

int i = 0;

while (arr[i] >= 0)

{

i++

}

location = i;

This program will work as intended

A. always

B. never

C. whenever arr contains at least one negative number ANSWER

D. whenever arr contains at least one nonnegative integer

E. whenever arr contains no negative integers

n Refer to the following code segment. You may ssume that arr is an array of int values.

int sum = arr[0], i = 0;

while (i < arr.length)

{

i ++;

sum += arr[i];

}

Which of the following will be the result of executing the segment?

A. Sum of arr[0], arr[1], ..., arr[arr.length-1] will be stored in sum.

B. Sum of arr[1], arr[2], ..., arr[arr.length-1] will be stored in sum.

C. Sum of arr[0], arr[1], ..., arr[arr.length] will be stored in sum.

D. An infinite loop will occur.

E. A run-time error will occur. ANSWER

n The following code fragment is intended to find the smallest value in arr [0]...arr[n-1].

//Precondition: arr[0]...arr[n-1] initialized with integers, arr is an array, arr.length = n

//Postcondition: min = smallest value in arr[0]...arr[n-1].

int min = arr[0];

int i = 1;

while (i < n)

{

i++;

if (arr[i] < min)

min = arr[i};

}

This code is incorrect. For the segment to work as indicated, which of the following modifications could be made?

I Change the line

int i = 1;

int i = 0;

//make no other changes.

II Change the body of the while loop to

{

if (arr[i] < min)

min = arr[i];

i++;

}

//make no other changes

III Change the test for the while loop as follows

while (i <= n)

//make no other changes.

A. I only

B. II only ANSWER

C. III only

D. I and II only

E. I, II, and III

Part 3: GridWorld Case Study

n Assume that variable grid is a properly initialized Grid. Which of the following expressions evaluate the number of occupied locations in grid?

A. grid.numRows() * grid.numCols()

B. grid.getOccupiedLocations()

C. grid.getOccupiedLocations().size() ANSWER

D. grid.getOccupiedAdjacentLocations().size()

E. grid.toString().size()

n Assume that variable oneBug is facing north in its grid. Under which of the following conditions would the method call oneBug.canMove() return false?

I. The location to the north of the bug is empty.

II. The location to the north of the bug contains a flower.

III. The location to the north of the bug contains a rock.

A. I only

B. II only

C. III only

D. I and II ANSWER

E. II and III

n Which of the following methods is defined in the Bug class because it is required to correctly extend the Actor class?

A. act

B. turn

C. move

D. canMove

E. No methods are required to be implementd in the Bug class to correctly extend the Actor class ANSWER