AP Comp Sci Final Review (part I)

Class, objects, arrays and Strings are examples of:

• nonprimitive data types

• primitive data types

• inheritance

• arrays

• recursion

Downcasting, super(), super, extends, interface and implements are examples of:

• nonprimitive data types

• primitive data types

• inheritance

• arrays

• recursion

enhanced for, nested loop, index and length are examples of:

• nonprimitive data types

• primitive data types

• inheritance

• arrays

• recursion

self-calling, base case and StackOverflowException are examples of:

• nonprimitive data types

• primitive data types

• inheritance

• arrays

• recursion

class MCQReview{

int x;

int y;

MCQReview(int x, int y){

this.x = x;

this.y = y; }

void method(){

x += x++ - y/2 + ++y; }

void display(){

System.out.println("x is: " + x);

System.out.println("y is: " + y); }

public static void main(String[] args){

MCQReview m1 = new MCQReview(10,20);

m1.method();

m1.display(); }

}

  What will be the output of the above code segment?

• x is: 32

  y is: 20

• x is: 30

  y is: 21

• x is: 32

  y is: 21

• x is: 30

  y is: 20

• x is: 31

  y is: 21

Answer explanation

x = 10, y =20

x += x++ - y/2 + ++y;

According to operator precedence and operator associativity,

x = x+ (x++ - y/2 + ++y);

x = 10 + (10 - 20/2 + 21) // internally y and x are incremented by 1

x = 10 + ( 10 - 10 +21) = 10 + (0 +21) = 31

x ++ will first substitute and then increment, whereas ++y will first increment and then substitute.

class MCQReview2{

int x; static int y;

void display(){

System.out.println("x is: " + x);

System.out.println("y is: " + y); }

public static void main(String[] args){

MCQReview2 m1 = new MCQReview2();

MCQReview2 m2 = new MCQReview2();

m1.x = 2;

m1.y = 3;

m2.x = 4;

m2.y = 5;

m1.display();

m2.display(); } }

What will be the output of the above code segment?

• x is: 4

  y is: 3

  x is: 4

  y is: 5

• x is: 2

  y is: 3

  x is: 2

  y is: 3

• x is: 2

  y is: 5

  x is: 4

  y is: 5

• x is: 2

  y is: 4

  x is: 3

  y is: 5

• x is: 2

  y is: 3

  x is: 4

  y is: 5

Answer explanation

x is: 2

y is: 5

x is: 4

y is: 5

The variable y, being static, is a shared copy for all the objects. If one object alters the value, it will modify for both of the objects. The variable x is nonstatic, which means that it is an instance variable, a different copy for different objects.

Assuming that a and b are declared as valid integer values, which of the following is an equivalent statement for the Java statement below?

(x > 5 && x < 8) || (x > 0 || y < 0)

• ((x > 0) || (x > 5 && x < 8)) || (y < 0)

• (x > 5 && x < 8) && (x > 0)

• (y < 0) || (x > 5 && x < 8)

• (x < 0 && y > 0) && (x < 5 || x > 8)

Answer explanation

((x > 0) || (x > 5 && x < 8)) || (y < 0)

Using the commutative property, the terms can be switched while maintaining the value. The || operator is used with the commutative property, and the expression with && remains together to follow the laws of logic.

Which of the following code segments will produce the output given below?

Output:

1 22 333 4444 55555 

• for (int i = 1; i <= 5; i++) {

  for (int j = i; j > 0; j--) {

  System.out.print(i);

  }

  System.out.println();

  }

• for (int i = 1; i < 6; i++) {

  for (int j = 0; j < i; j++) {

  System.out.println(i);

  }

  }

• for (int i = 1; i < 5; i++) {

  for (int j = i; j > 0; j--) {

  System.out.print(i);

  }

  System.out.println();

  }

• for (int i = 0; i < 5; i++) {

  for (int j = 0; j < i; j++) {

  System.out.print(i);

  }

  System.out.println();

  }

• for (int i = 0; i < 5; i++) {

  for (int j = 0; j < i; j++) {

  System.out.print(i+1);

  }

  System.out.println();

  }

Answer explanation

for (int i = 1; i <= 5; i++) {

for (int j = i; j > 0; j--) {

System.out.print(i);

} System.out.println();

}

The outer loop executes the inner loop six times. The inner loop takes care of the digits to be printed and the number of times they are to be printed on the screen. In every line, the digit is same as the line number. After printing the digits the specified number of times, a new line is printed.

import java.util.*;

public class MCQReview3 {

public static void main(String[] args) {

String[] list = {"John","Karen","Larry","Samuel"};

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

for(int i = 0; i < 12; i++) {

names.add(list[i % list.length]); }

for(int i = 0; i < 12; i++) {

if(names.get(i).equals("Larry")) {

names.remove(i); }

}

}

}

The above code segment shows an error on compilation. Which of the following is the reason for the error?

• excess use of computer memory

• incorrect use of the % operator as an index in add(list[i % list.length]

• infinite loop in one of the two for loops

• overrun of the index mentioned in the second for loop

• error in the get() method parameter

Answer explanation

The second loop will show an error due to array elements getting removed. This will decrease the size of ArrayList, resulting in an ArrayIndexOutOfBounds run-time error.

Consider the code segments with a 2D array shown below.

Which of the following code segments will perform a row-wise traversal without any errors?

I.

int [][] myArray ={{1, 2, 3,4},{5,6,7,8},{9,10,11,12}}; for(int i =0;i<myArray.length; i++) for(int j=0;j<myArray[i].length; j++){ System.out.print(myArray[i][j] + " "); }

II.

int [][] myArray ={{1, 2, 3,4},{5,6,7,8},{9,10,11,12}}; for(int i[][] : myArray) System.out.print(i + " ");

III.

int [][] myArray ={{1, 2, 3,4},{5,6,7,8},{9,10,11,12}}; for(int i[] : myArray) for(int j : i) System.out.print(j + " ");

• I only

• II only

• III only

• I and II

• I and III

Answer explanation

Code segment I has no errors, as it is a nested loop traversing through a 2D array, row-wise and column-wise.

Code segment III also has no errors, as the enhanced nested loop is traversing through a 2D array.

Code segment II has an error in that it has a type mismatch: You cannot convert from element type int[] to int[][].