Chapter 2 Review by Marrien Gomez

Calling a Non-Void Method

mgomez233_1 — 2022-09-28 05:42:56 UTC

The void method will not return any value. It can be used to change the parameters of an object without creating a new object.

Objects: How to Create/Store Objects

mgomez233_1 — 2022-09-28 05:43:18 UTC

Create Objects:
- make a constructor
- ConstructorName objectName = new ConstructorName().
- Enter the information about the argument in the parentheses to match the constructor.

Wrapper Classes

mgomez233_1 — 2022-09-28 05:43:25 UTC

A Wrapper class is a class whose object wraps or contains primitive data types. We can wrap a primitive value into a wrapper class object.

    Integer num = Integer.valueOf(23);
    Double num2 = Double.valueOf(5.55);

    // converts into primitive types
    int a = num.intValue();
    double b = num2.doubleValue();

    System.out.println("The value of a: " + a);
    System.out.println("The value of b: " + b);
  }

Math Class

mgomez233_1 — 2022-09-28 05:43:31 UTC

Methods to know:
- double abs(double x); int abs(int x) ;

absolute of number

- double sqrt(double x)

square root of number

- double random()

random number from 0-1

- double pow(double base, double exponent)

...to the power of...

- (int) (Math.random() * (total # of choices));

Remember that Java is base 0 so if 10 is entered as the number of choices then a number between 0-9 will be generated.
Between two positive numbers: ◦ (int) (Math.random() * (total # of choices)) + starting number;

Overloading

mgomez233_1 — 2022-09-28 05:43:37 UTC

Overloading in Java is the ability to define more than one method with the same name in a class.

Overloading Example:
Private String name;
Private int age;

Public Person(String n)
{
Name = name;
Age = unknown;
}

Public Person(String n, int a)
{
Name = n;
Age = a
}

Person Natalie = new Person(“Marrien”);
Person Maggie = new Person(“Gomez”, 17);

Void Method Examples

mgomez233_1 — 2022-09-28 05:43:47 UTC

Private int width;
Private int height;

Public Rectangle(int wid, int hei)
{
Width = wid;
Height = hei;
}

Pubic void changeWidth(int wid)
{
Width = wid;
}

Rectangle rect1 = new Rectangle(10, 5);
rect1.changeWidth(6);

//code changes width from 10 to 6//

String Object

mgomez233_1 — 2022-09-28 05:43:58 UTC

Strings are objects that consist of a set of characters(letters, numbers, punctuation, etc.).

How to create a String:

String name = “word”; (In quotation marks!!)

Java will automatically number each character in a String, starting from 0. That number is called the Index. For example:

String name = “word”;

|w|o|r|d|<— String Characters

|0|1|2|3|<—- Index

Other things to note about Strings:

- They are immutable, which means they can’t be changed in the traditional sense like int and double values can. Instead, they must be re-assigned to a new String value. Even though the String won’t point to the same memory address anymore, the old value still exists in memory though.

- Because Strings are objects, they have methods!

String Method

mgomez233_1 — 2022-09-28 05:44:09 UTC

- String.length()

Returns the number of characters in a String

- String.charAt(int index)

Returns the char at the index value given

- String.substring(int from, int to)

Returns a String from the first index up until but not including the last index.

- String.substring(int from)

Returns a String from the first index given until the end of the String

- String.indexOf(String str)

Returns an int of the index value of the first iteration of the given String inside the String object the method’s being called on

- String.equals(String other)

Compares the String object to a given String and Returns a boolean value of true they’re the same, false otherwise.

- String.compareTo(String other)

Compares the String object to a given String and returns an int value based on the first discrepancy between the two Strings, either in lexicographical order or if no difference there, in length.