Objects with Strings

Question 1

Object

Answer 1

Is an in-memory data structure that combines state and behavior into a usable and useful abstraction.

Question 2

Class

Answer 2

Source code that defines how to create an object and what state and behavior that object will have.

Question 3

Steps to instantiate or create an Object from a Class

Answer 3

1. Declare a variable to hold the object. The class will be the data type.
2. Instantiate a new object from the class using the new keyword.
3. Initialize variables inside the object with initial values using the constructor.

Question 4

Data Types Memory

Answer 4

Value Type - primitive

Reference Type - Object

Question 5

Value Type (primitive)

Answer 5

Reference a single static space in memory to hold the value. This memory is allocated on the stack.
Only 8 value types: byte, char, short, int, long, float, double, and boolean.

Question 6

Reference Type (Object)

Answer 6

Holds a reference to where the object is located in free-floating, dynamic memory, the heap. Everything except the 8 value types is a reference type.

Question 7

Pass by Value

Answer 7

Pass the value of the variable.

Question 8

Is Java Pass by Value or Pass by Reference?

Answer 8

Java is always Pass by Value. Java passes the value on the Stack when passing a variable to a method.

Question 9

Immutability

Answer 9

An object whose state cannot be changed after it is created. A string is immutable, meaning after a string is created the value cannot be changed, but instead, a new String must be created with the new value.

Question 10

Null

Answer 10

Not the same thing as empty. Refers to no value on the Stack. Empty refers to the value of an existing object on the Heap.

Question 11

Object Equality

Answer 11

The value of Reference Types (Objects) cannot use == to compare the value of objects, instead they use the .equals() method.

Question 12

Reference Equality ( == )

Answer 12

The equality operator compares the value of 2 variables on the stack. For objects, this is the reference to the Object on the heap

Question 13

Value Equality ( .equals() )

Answer 13

The .equals() method compares the value of Objects on the Heap

Question 14

Object characteristics

Answer 14

1. Live in the computer’s memory and only exist while a program is executing.
2. Is distinct and separate from every other object in a program.
3. Not written in a source code. Instead, they are what is created when a program executes, based on the source code.
4. Everything in Java is an Object, except the primitive data types (byte, short, int, long, float, double, boolean, and char).

Question 15

Class characteristics

Answer 15

1. Is a blueprint for an object.
2. Classes don’t exist when the program is running, they only exist in source code.
3. Defines a Data Type, which makes everything in Java a Data Type.

Question 16

Pass by Reference

Answer 16

Pass the memory location of the value.

Question 17

There are 2 types of Equality for Objects in Java

Answer 17

1. Reference Equality ( == ).

2. Value Equality ( .equals() ).

Question 18

Objects behaviors represented by

Answer 18

Methods

Question 19

String methods

Answer 19

contains( string ), startWith( string)
endsWith( string ), indexOf( string ), replace( string1, string2), toLowerCase()
toUpperCase(), split( str ), equals( string )
equalsIgnoreCase( string ), trim()