Inheritance & Polymorphism
Given the following classes:
class A {}
class B extends A {}
class C extends B {}
On what line does the following code throw an error, if any?
A obj1 = new C();
C obj2 = obj1;
Object obj3 = obj1;
2
What is the output of the following code?
int[] arr = { 1, 2, 3, 4, 5 };
for (int i = 0; i <= arr.length; i++)
System.out.println(arr[i]);
ArrayIndexOutOfBoundsException
What is the value of the following expression?
"abc".compareTo("abcd")
-1
How many times will the while loop be executed when calling binarySearch(new int[]{1, 2, 3, 4, 5, 6}, 10)?
public static int binarySearch(int[] arr, int target) {
int left = 0;
int right = arr.length - 1;
while (left <= right) {
int mid = left + (right - left) / 2;
if (arr[mid] < target)
left = mid + 1;
else if (arr[mid] > target)
right = mid;
else if (arr[mid] == target)
return mid;
}
return -1;
}
3 times
What is the value of the expression 5 / 2?
2
What problems are there with the following code?
interface A {
int data = 3;
void doSomething();
}
class B extends A {
public static void main(String[] args) {
System.out.println("Hello World");
this.doSomething();
}
}
What is the missing expression in this function that allows the code to function?
public int sum(int[][] arr) {
int s = 0;
for (int r = 0; r < arr.length; r++)
for (__________)
s += arr[r][c];
return s;
}
(int c = 0; c < arr[c].length; c++)
What is the value of the following expression?
Integer.MIN_VALUE - 1
2147483647 (Integer.MAX_VALUE)
What sorting algorithm is implemented in the following code?
public static void sort(int arr[]) {
int n = arr.length;
for (int i = 0; i < n-1; i++) {
int idx = i;
for (int j = i+1; j < n; j++)
if (arr[j] < arr[idx])
idx = j;
int temp = arr[idx];
arr[idx] = arr[i];
arr[i] = temp;
}
}
Selection sort
What is the range of possible values that can be printed as a result of executing the following statements?
int x = (int) Math.random() * 10;
System.out.println(x);
0 only
A obj0 = new A();
A obj1 = new B();
A obj2 = new C();
obj0.print();
obj1.print();
obj2.print();
What will the previous code output, given the following classes?
interface A {
void print();
}
class B {
void print() {
System.out.println("Printing from B");
}
}
class C {
void print() {
System.out.println("Printing from C");
}
}
Cannot instantiate the type A
What will this function do when it is called on 10x10 array of values?
public void run(int[][] arr) {
for(int[] rows : arr) {
for(int n : arr) {
n = n + 1;
}
}
}
Nothing.
What is the output of the following code?
String str = "Hello World"; System.out.println(str.substring(4, 5) == str.substring(7, 8));
false
How many times will the inner while loop of the following insertion sort implementation be called when sorting the array { 7, 2, 4, 6, 1, 9 }.
static void insertionSort(int[] arr) {
for (int i = 1; i < arr.length; i++) {
int n = arr[i];
int j = i;
while (--j >= 0 && arr[j] > n)
arr[j + 1] = arr[j];
arr[++j] = n;
}
}
7 times
On which line is there a compile-time error in the code?
class Main {
void run(String... strs) {
for (String s : strs)
System.out.println(s);
break;
}
}
Line 4
A obj1 = new C();
A obj2 = new A();
C obj3 = new C();
B obj4 = new B();
obj1.print(0);
obj2.print(0);
obj3.print(0);
obj4.print(0);
What is the output of the previous code, based on the following classes?
static class A {
void print(double x) {
System.out.println("1");
}
}
static class B extends A {
void print(double y) {
System.out.println("2");
}
}
static class C extends B {
void print(int z) {
System.out.println("3");
}
}
2
1
3
2
What is the output of executing run(2)?
public static int run(int x) {
if (x + 1 == run(x + 1))
return x;
else
return x - 1;
}
StackOverflowError
What will be printed as a result of executing the following code?
String str = "abcdef";
str.substring(2, str.indexOf("d"));
System.out.println(str);
abcdef
What will this array look like after 2 passes of merge-sort?
{7, 0, 2, 6, 5, 3, 1, 4}
{0, 2, 6, 7, 1, 3, 4, 5}
What will be printed to the console after executing the following code?
int[] arr = { 1, 2, 3, 4 };
int c = 0, s = 0;
for (int n : arr)
s += n;
c++;
System.out.println("Sum: " + s + ", count: " + c);
Sum: 10, count: 1
A obj = new C();
System.out.println(obj.getString());
Based on the following classes, what will the previous code output?
class A {
int x = 3;
String getString() {
return "a" + x;
}
}
class B extends A {
String getString() {
String str = super.getString();
x *= 2;
return "B" + x;
}
}
class C extends B {
String getString() {
return (double) x / 10 + super.toString();
}
}
0.3Ba36
What is the value of the expression recurse(2, 7)?
public static int recurse(int a, int b) {
int x = b + a;
int y = b - a;
if (x > y)
y = recurse(x, y);
return b + y;
}
-58
What is the output of the following code, assuming java.util.* has been imported?
Collection<int> list = new ArrayList<>();
list.add(1);
list.add(2);
list.remove(0);
System.out.println(list);
Error: unexpected type (required 'reference', found 'int')
What is the average-case O(n) time complexity of the following sorting algorithms?
Bubble, insertion, selection, merge, and quick sorts
Bubble, insertion, selection: O(n2)
Merge, quick: O(n log n)
What is the result of executing the following code?
int x = 0;
int y = 4;
System.out.println(++x == y-- || ++x < y && x++ == --y ? x : y);
3