Unit 2: Using Objects

Question 1

What is the keyword “new” ?

Answer 1

The “new” keyword is used to instantiate a new object.

Question 2

Proper String instantiation

Answer 2

String myString = new String(“Hello, World!”);

Question 3

Overloading

Answer 3

In Java, two or more methods may have the same name if they differ in parameters (different number of parameters, different types of parameters, or both). This is called overloading.
Ex. 
    public Rectangle(int rectWidth, int rectHeight)
    {
        width = rectWidth;
        height = rectHeight;
    }

    public Rectangle(int sidelength)
    {
        width = sidelength;
        height = sidelength;
    }

Question 4

What are parameters?

Answer 4

Data/arguments that are passed to a method.

Question 5

Wrapper Classes

Answer 5

Wrapper classes provide a way to use primitive data types (int, boolean, etc..) as objects.
ex.
int myInt = 10;
Integer myInteger = new Integer(myInt);

Question 6

Integer.parse

Answer 6

This method is used to get the primitive data type of a certain String.
Ex. Integer.parseInt(“11”); // Returns the int value 11

Question 7

Generating random numbers

Answer 7

The Math.random() method returns a random double from 0-1 excluding 1;
int randInt = (int) (Math.random() * (max - min) + min;

Question 8

What is an instance method?

Answer 8

A piece of code called on a specific instance (an object) of the class.

Question 9

What is a void method?

Answer 9

A void method is a method that does not have a return value. Usually, these contain a print statement or modify the variables within the object in some way.

Question 10

What defines a non-void method?

Answer 10

Non-void methods have a return statement. The method returns a certain data type and can be used as a variable of that data type.

Question 11

What is an Integer? What is its purpose?

Answer 11

A wrapper class that helps turn a primitive into an object and object into a primitive data type.

It can be used in lists and such because they only store data as objects, so the conversion from primitive to object is needed.

Question 12

Static Methods

Answer 12

Belong to the class rather than an instance of a class, therefore can be called without using an object.

Question 13

Instantiation

Answer 13

To create a new instance of an object.
ex.
Student Ryan = new Student();

Question 14

What are the different string methods?

Answer 14

name. concat(“value”) - returns a new string with “value” appended at the end of name
name. replace(“a”, “p”) - returns a new string with all instances of “a” in name replaced with “p”
name. toUpperCase()- Returns name as Upper Case Letters

Question 15

Can you change a string once it is created?

Answer 15

No! Strings are immutable, so they cannot be changed once they are created.
(If you wanted to change the value of a string, you would have to re-assign it!)

However, you can concatenate strings with one another to create a new string value!

Question 16

What are the different types of escape sequences?

Answer 16

" - allows for quotations in a string
\ - includes a backslash
\n - creates a line break
\t - adds a tab space

Question 17

.substring() String method.

Answer 17

Returns a piece of a String to a specified index. ex.
String myString = new String("Hello World");
System.out.println(myString.substring(6); // Returns "World"
System.out.println(myString.substring(0,3); // Returns "He". The second index is exclusive.