Question

Unit 7 Worksheet #2                                            Name:

1. Declare and initialize a 3 x 3 two-‐dimensional array that has the numbers 1-‐9 in it using an initializer list.

2. On the array below:

int[][] values = new int[4][10];

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

{

for(int c = 0; c < values[r].length; c++)

{

values[r][c] = (int)(Math.random()*51 + 50);

}

}

write the code to count and print the number of elements that are greater than 75.

3. What is the syntax for declaring and constructing an ArrayList?

4. What must be imported in order to be able to use an ArrayList?

5. Do you have to specify the type of data that will be stored in the ArrayList? Is it necessary to specify the amount of data that will be stored in the ArrayList? Explain.

6. What do the following Arraylist methodsreturn? size(), get(), remove(), set()

size()

get()

remove()

set()

7. Write the loop to print each of the ArrayLists:

ArrayList<String> list1 = new ArrayList<String>();

list1.add(“hello”);

list1.add(“there!”);

Answer 1

thanks for the question.

Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change.If you are satisfied with the solution,

please rate the answer.

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import java.util.ArrayList;

public class Unit7 {

    public static void main(String[] args) {

        //Declare and initialize a 3 x 3 two-‐dimensional array that has the numbers 1-‐9 in it using an initializer list.
        int[][] digits = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};

        //On the array below:
        int[][] values = new int[4][10];
        for (int r = 0; r < values.length; r++) {
            for (int c = 0; c < values[r].length; c++) {
                values[r][c] = (int) (Math.random() * 51 + 50);
            }
        }
        //write the code to count and print the number of elements that are greater than 75.
        int greaterThan75Count = 0;
        for (int r = 0; r < values.length; r++) {
            for (int c = 0; c < values[r].length; c++) {
                greaterThan75Count += values[r][c] > 75 ? 1 : 0;
            }
        }
        System.out.println("There are "+greaterThan75Count+" numbers greater than 75 in the array");

        ArrayList<String> list1 = new ArrayList<String>();
        list1.add("hello");
        list1.add("there!");
        for(String item:list1){
            System.out.println(item);
        }
    }

    //What is the syntax for declaring and constructing an ArrayList?
    // We can replace Object by any class name
    ArrayList<Object> arrayList = new ArrayList();

    //What must be imported in order to be able to use an ArrayList?
    // answer : import java.util.ArrayList;

    //Do you have to specify the type of data that will be stored in the ArrayList?
    // answer : By typing in the class name inside the angle brackets. e.g String
    ArrayList<String> stringList = new ArrayList<>();
    // Is it necessary to specify the amount of data that will be stored in the ArrayList? Explain.
    // answer: arraylist are resizable, we dont need to declare the size
    // it automatically resizes to accomodate new objects

    //What do the following Arraylist methodsreturn? size(), get(), remove(), set()
    // size() : returns the total elements in the arraylist
    // get() : returns the element at a particular index, it takes an int value
    // remove() : removes an object if the equals() matches for that object
    // set() : set a value at a particular index



}

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