AP CSA - Unit 6 - Arrays

Arrays are immutable. Immutable means:

• changeable
• dynamic

• flexible
• unchangeable

Answer explanation

In computer science, "immutable" means something that can't be changed after it's made. Once created, its value or state stays the same always. For example, in Java, a String is immutable. If you make a String with certain text, you can't change that text later. You need to make a new String for a different text.

Which of the following is the correct way to initialize an array in Java?

I. int[] num = new int[3];
II. int[] num = new array [1,2,3];
III. int[] num = {1,2,3};

• I only

• II only

• III only

• I and II

• I and III

Which of the following is the correct way to initialize an array in Java?

I. String [] str = new String[3];
II. String str [ ] = {"hi","hello"};
III. String [] str = {'1','2','3'};

• I only

• II only

• III only

• I and II

• I and III

Answer explanation

Though the syntax looks a little strange, the code in line II still works correctly.

Consider the following code segment:

int[] num = new int[5];

System.out.println(num[3]);

What is the output of the above code?

• 3

• null
• ArrayIndexOutOfBounds

• 0
• Compile-time Error

Answer explanation

When an array is created, but is not assigned any values, it is automatically filled with zeroes.

Therefore,
int[] num = new int[5];

Will look like this:
{0, 0, 0, 0, 0}

Consider the following code segment:

double[] num = new double[5];

System.out.println(num[3]);

What is the output of the above code?

• 3.0

• null

• ArrayIndexOutOfBounds

• 0.0

• Compile-time Error

Answer explanation

When an array is created, but is not assigned any values, it is automatically filled with zeroes.

Therefore,
int[] num = new int[5];

Will look like this:
{0, 0, 0, 0, 0}

Consider the following code segment:

String[] str= new String[5];

System.out.println(str[3]);

What is the output of the above code?

• 3

• null
• ArrayIndexOutOfBounds

• 0
• Compile-time Error

Answer explanation

When an int array is declared but not initialized it is automatically filled with zeroes. However, when a string array is declared but not initialized, it is automatically filled with null values.

Therefore,
String[] str= new str[5];

Will look like this:
{null, null, null, null, null}

int number = 13;

int[] values = {0, 1, 2, 3, 4, 5};

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

{

number += values[i];

}

System.out.println(number);

What number is printed as a result of executing the code above?

int total = 3;

int[] values = {8, 6, 4, -2};

total += values[total];

total += values[total];

System.out.println(total);

What number is printed as a result of executing the code above?

int[] values = {7, 9, 4, 1, 6, 3, 8, 5};

for (int i = 3; i < values.length; i += 2)

{

System.out.print(values[i - 2]);

}

What output is shown by executing the code above?

int[] nums = {0, 0, 1, 1, 2, 2, 3, 3};

for (int i = 3; i < nums.length; i++)

{

nums[i + 1] = i;

}

What values are stored in array 'nums' after executing the code segment?

• ArrayIndexOutOfBoundsException

• {2, 2, 3, 3, 4, 4, 5, 5}

• {0, 0, 1, 3, 5, 7, 9, 11}

• {0, 0, 1, 1, 3, 4, 5, 6}

• {0, 0, 1, 2, 2, 3, 4, 5}