Basics_Java Flashcards

Question

What is JDK?

Answer 1

**Java Development Kit** **Software Development Environment** Compiler Reusable Code Java Run Time Environment

Answer 2

120 Million TV sets Every blue-ray device

Answer 3

The JVM has **two primary functions**: to allow Java programs to run on **any device** or **operating system** (known as the "**Write once, run anywhere**" principle), and to **manage and optimize** **program memory**. When Java was released in 1995, all **computer programs** were **written to a specific operating system**, and program memory was managed by the software developer. So the JVM was a revelation.

Answer 4

$101,929 USD Java is everywhere. There are many opportunities to get hired as a professional Java developer.

Answer 5

Build clean code Fix bugs and errors Understand types Create algorithms Package and deploy programs so other people can use them!

Answer 6

Variables and Constants Primitive and Reference Types Casting Numbers, Strings and Arrays Reading Input

Answer 7

A variable is how we temporarily store data in computer memory.

Answer 8

The **name of a variable** "=" is **assignment operator**

Answer 9

Copy the value of one into another

Answer 10

Camel case! lowercase first letter Uppercase other letters! Ex. int **h**er**A**ge = 30

Answer 11

int - allow us to store values up to 2 billion long - store numbers greater than 2 billion double - storing values with decimal values float - storing values decimal values char - storing characters boolean - store true or false

Answer 12

always use meaningful, descriptive names

Answer 13

add and L after the value. By default Java compiler recognizes a number as an integer. Put an L after to tell Java compiler its a long!

Answer 14

Java see's numbers with decimals as doubles by default. We have to add a suffix to represent the number as a float Add "F"

Answer 15

surround **single characters** by **single quotes** string represents a series of characters

Answer 16

objects + their members (data/functions)

Answer 17

Type conversion

Answer 18

use the **new operator** Allocate memory

Answer 19

**First,** allocate some memory to store the point object **Next**, allocate a separate part in memory to store a reference (the address) to the point object **Finally,** assign this reference to the variable name

Answer 20

**Value** is **stored** in the **variable at that memory location** x and y are **completely independent** of each other

Answer 21

The **reference** to **pointOne** object in memory, **not the point object**

Answer 22

When we declare a **primitive variable** like a byte the value we assign is **stored in that memory location**. When we use a **reference type** our variable **holds the reference (address) of the object** in memory **not the actual value**.

Answer 23

Variable holds the **address or reference** of the object in memory, **not the actual value**. Two variables can **reference the same object**.

Answer 24

Remember, reference types are copied by references. primitives are copied by values and are completed independent of each other.

Answer 25

Strings are reference types. We use a short way to create them (can omit the new operator) Strings are a class so we can access methods with the dot operator!

Answer 26

because strings are a class, we can access methods like ends with, length, indexOf(), replace etc. Ex. check length of user input string Ex. give the index of the first character

Answer 27

**parameters** are the holes we define in our methods. **arguments** are actual values we pass to these methods.

Answer 28

Immutable We cannot mutate them, we cannot change them any methods that modify a string create a new string object

Answer 29

the trim method used if a user types unnecessary white spaces in form fields

Answer 30

**Members** properties (data) or functions

Answer 31

**An instance** of **a** **class** **A reference type** **object/classes** have **members we can access** using the **dot operator**

Answer 32

Reference types We need the new operator we can access elements or items in the array via an index

Answer 33

Java returns the string of the address in memory to see the actual items in the array we must use the array's class

Answer 34

"sout" + Tab

Answer 35

String is a reference type however, we have a shortcut Can omit the new operator JavaRuntime will handle

Answer 36

Use the array class .toString method there is a .toString for every primitive type

Answer 37

**Reference types** use the **new operator** to allocate memory for the reference variable **Primitive** **types** don't require us to **allocate memory** java run time environment does this for us!

Answer 38

**\"** = \"fileNames\" **\n** = new line **\** = \ **\t** = tab

Answer 39

Store a list of items: numbers people message

Answer 40

Defined in Java.util **Has useful methods:** Arrays.toString

Answer 41

Multi-dimensional array's Can create a 2D array to store a matrix or a 3D array to store data for a cube These are useful for scientific computations Ex. two rows and three columns

Answer 42

all CAPS add the final

Answer 43

All the same in math like "+" "-" "\*" "/"and "%" (modulus or remainder) / gives a whole number

Answer 44

In Java.util package Arrays Class Arrays.toString method - returns string rep of array defined for all primitive types

Answer 45

A piece of code that produces a value

Answer 46

By default Java returns integer values for integer division. Cast our input into double #s are called **operands**

Answer 47

cast the numbers into a double

Answer 48

if we want to increment a value we can add ++ Can say ++x (prefix) OR x++ (suffix) same value

Answer 49

**First**, Java will **increment x by one** x (=2) **Then**, Java will **copy x value** to y (=2)

Answer 50

add final keyword cannot change value later in program

Answer 51

**First,** Java assigns the value of x (=1) to y **Then,** increments x by one x (=2)

Answer 52

if increment as a suffix x++ first value of x is copied to y then x is incremented by 1 if increment as a prefix ++x first, x is incremented by 1 then copied to y

Answer 53

We can increment by 2 x+=2 will increment x by 2 and copy into x

Answer 54

If we want a value calculated first, we can put it in parentheses.

Answer 55

Automatic casting / automatic conversion Java allocates an anonymous variable in memory that variable is another primitive type (byte, int, long) Java copies value into this new anonymous variable If the value can be converted into a bigger type, Java automatically does this for us. short = two bytes int = four bytes

Answer 56

when there is no change for data loss when we are going from a smaller to a larger data type

Answer 57

convert x to an integer w/o decimal point x will be added to 2 result = 3

Answer 58

between compatible types all number types cannot cast a string to a number

Answer 59

For **all primitive types**, have wrapper classes reference type defined in java.lang reference classes have methods like parseInt() which takes a string returns a short or int

Answer 60

in most GUI data from the user is received as a string! If we have text boxes or drop down lists almost always we receive data as strings we must convert these strings to numerical representatives

Answer 61

The greater of two values

Answer 62

Control + Shift + /

Answer 63

A random number (float) to set between a value, multiple by range

Answer 64

pass the random method as an argument to the round method explicitly cast the value into an integer

Answer 65

use the scanner class Java will do implicit casting to make the int value of age into a string and concatenate

Answer 66

Shift + F6

Answer 67

using the scanner.next ( ) method

Answer 68

use the scanner.nextLine ( )

Answer 69

**Shift + F6**

Answer 70

use the dot operator to access members (methods) of the string object call the trim method then store value in the name variable

Answer 71

First attempt No input validation Written as **procedural code**

Answer 72

controlling the **flow of execution** of our programs

Answer 73

controlling the **flow of execution**

Answer 74

**executing code repetitively** Ex. **For loops** **For each** **While loops** **Do-while**

Answer 75

**Comparison operators** comparing values Ex. **\>= \<= ==** **Logical operators** implementing real-world rules Ex. **&& != ||** **Conditional statements** making decisions around code execution in our programs Ex. **If, switch** statements **Loops** executing code repetitively Ex. **for, while** loops

Answer 76

Used for **comparing values** greater than equal to less than \>= \<= ==

Answer 77

To compare primitive values Ex. is x and y the same?

Answer 78

a boolean expression returns true/false represented with two equal signs "=="

Answer 79

A boolean expression != returns a true/false

Answer 80

Making **decisions** in our **programs** ## Footnote **Ex. If statements**

Answer 81

\>= (greater than or equal) \<= (less than or equal) These return boolean (true/false) values

Answer 82

Evaluates from left to right **First**, it looks at the leftmost condition if false, doesn't look at other conditions, returns false

Answer 83

Implementing **real-world rules** & || !

Answer 84

the assignment operator we use it to assign a value to a variable

Answer 85

The or || operator is true if at least one condition is true.

Answer 86

To reverse a value if the value hasCriminalRecord = false; !hasCriminalRecord returns true

Answer 87

use a boolean operator wrap in ( ) to be clear

Answer 88

Remove { } braces from single statement clauses put else if on the line below ending curly brace ( { )

Answer 89

It's **only available** within that **code block** we **cannot access** outside

Answer 90

Use the **Scanner class**! Read from the **console**: **new Scanner (System.in)**

Answer 91

If statement three clauses look at format Hierarchy parent w/ two children } else if (condition) } else

Answer 92

They allow build programs to make decisions based on certain conditions? Ex. Printing messages on console based on certain conditions

Answer 93

A boolean value if the condition is true, the statements in curly braces are executed.

Answer 94

a section parent and children hierarchy If only one line of code in the if statement can omit the { } Technically, people say always have { }

Answer 95

The variable hasHighIncome is only available within the curly braces!

Answer 96

Declare the variable outside the if-statement set the value to true within the statement \*\*this code look amateurish

Answer 97

we can set the variable to an initial value. Or we can set our variable to an expression and eliminate the if-statement entirely if the expression is true it will evaluate to true, otherwise it will evaluate to false.

Answer 98

To make it more clear now it's clear that on the right side of the assignment operator we have a boolean expression

Answer 99

This kind. One way to fix this is give the variable an initial value This can be simplified even further using a ternary operator!

Answer 100

**Condition (boolean expression)**? value #1 : value #2 We start with our condition then we add a "?" if the first condition is true, value after "?" is assigned otherwise the value after ":" is assigned String className = income \> 100\_000 ? "first" : "economy"

Answer 101

To execute different parts of code depending on the value of the expression. like an if-statement

Answer 102

Java will **continue to execute** the **other cases** once it **evaluates a break statement** it jumps out of the **switch statement**

Answer 103

add a **break** after **each case** **default** will execute if **no cases are met**

Answer 104

Put the most specific statements on top Java evaluates top to bottom

Answer 105

It has a nested structure. Mosh prefers a flat structure. Additional nested structures make the code hard to read

Answer 106

1. **Declare a counter variable** ( i , j , k) - loop counters 2. **Declare a boolean expression** - declare how long loop is executed 3. **Increment loop counter** \*If a single expression, don't need curly braces but if multiple statements must declare a code block

Answer 107

1. first it initializes i to zero (first statement) 2. Then it evaluates the boolean (if true, executes code block) 3. At end of loop, control moves to increment i to ++

Answer 108

Output: Hello World 5 Hello World 4 Hello World 3 Hello World 2 Hello World 1

Answer 109

start with a **condition** if the condition is true, evaluate and assign value after "?" otherwise, if the condition is false, evaluate and assign value after " : "

Answer 110

Because of the way **Java executes** the if statement Sequentially executes Put most complex case first Simpler cases follow

Answer 111

initialize a **loop variable** **set a condition** for termination **execute code** in the **block** **decrement the counter variable**

Answer 112

**For Loop:** We know how many times we want to execute one or more statements **While Loop:** We don't know exactly how long to execute

Answer 113

Similar to while loops Gets executed at **least once** **the condition gets checked last**

Answer 114

**While loops** check **conditions first**, if false it never gets executed. **do..While loops** we check the **condition last**! Do...while loops are rare and **we often use while loops**!

Answer 115

it **ignores everything** after and **break statement** and **exits out of the loop**.

Answer 116

Set counter to **count down** or **count up**!

Answer 117

Java sees the continue statement moves the control to the beginning of the loop all statements after are ignored

Answer 118

set the **while condition** to (true) the loop is executed forever until the **break conditio**n is met! make sure to use a **break statement** otherwise, you have an **infinite loop**!

Answer 119

**while (true)** include a **break statement!** otherwise, you have **an infinite loop**!

Answer 120

use "**for**" keyword a **counter variable** and **initialize** **boolean expression** determines how many times loop is executed increment the counter variable

Answer 121

When **iterating** over an **array or collection**! Replaces **a for loop** we don't have to **write a numeric counter** we don't have to write a **boolean expression** we don't have to **increment our counter**

Answer 122

inside for ( ) include the **type** of array (collection) we are iterating over declare a variable to hold the value of each item one at a time in our collection per iteration. **Ex**.

Answer 123

**For each loop:** 1. **Forward only** - Cannot iterate end to the beginning. 2. **Don't have access to index** - loop variable stores only one item **For Loop:** can access **values** by **index**

Answer 124

Set the counter variable to length of the array as long as i is greater than 0 print value at the index of counter decrement counter

Answer 125

**Initialize** the **variables** to **zero** **outside the loops!**

Answer 126

**Knowing how to** **write good code**: **Code** that is **clean and expressive**

Answer 127

Mosh puts a lot of emphasis on **clean code**!

Answer 128

The most **important techniques** for writing **clean code.**

Answer 129

It's just the same as if we declared a **local variable** inside it's like a **local variable** **inside the method**

Answer 130

camelCase for **method name** and **parameters** **parameter** is like a **local variable** inside **the method**

Answer 131

Change return type call the method from the main class Give it an argument store the return value in a variable

Answer 132

**cameCase** for **parameter identifiers** separate with a **comma**

Answer 133

Change return type from void to String return keyword to return value \*when calling this method can store the return value in a variable

Answer 134

Changing the structure of our code without changing its behavior. Extracting certain methods and putting them in other methods. **Extracting methods** **Refactoring Repetitive Patterns**

Answer 135

1. **Look for conceptually close code** - lines of code that always go together. Bring lines together into a separate private method. Can re-use method in the future! 2. **Repetitive patterns in code** - code that uses repetitive loops asking the same questions using similar patterns

Answer 136

**5-10 lines of code!** No more than **20 lines**!

Answer 137

Create a **method** for **calculating mortgage** Call this **method** in the **main class**

Answer 138

**Right-click** the lines Select **Refactor** Select **Extract** Choose **Method**

Answer 139

Create a **readNumber** method!

Answer 140

Syntax errors. Prevent us from compiling our applications. Happen when we don't follow grammar or syntax of Java. Easy to **find and fix**!

Answer 141

Stackoverflow.com! Professional programmers and enthusiasts! Search for error message 99% of time you can find a page on this error!

Answer 142

Debugger! **Execute** our code **line by line**. Look at the **value** of **various variables**!

Answer 143

**Compile-time:** syntax or grammar errors, use IntelliJ or StackOverflow **Run-time errors:** use Debugger to look at variables

Answer 144

1. Forget to **specify the data type** of variables 2. Forget to **add a semi-colon** to the end of statements! 3. Call a **method** without using ( ) 4. Print a **string** without double quotes 5. **misspell or incorrectly capitalize** a variable name (Java is case sensitive) 6. using **reserve keywords** for identifiers 7. using a **single "=" to compare values**"=="

Answer 145

**Yes** and **No**. **No,** it's **open-source**. **Yes**, there are additional **features/support** you can **pay to use.**

Answer 146

An area where we can see all the methods that were executed in reverse order! Useful for debugging large applications! Can set a breakpoint and watch all the methods to get there!

Answer 147

can **set watches** to view **specific variable values**

Answer 148

**Additional steps** outside the **scope of this course.**

Answer 149

Another **layer of abstraction** **above packages**

Answer 150

need to package it into a .jar file Java Archive - contains all code for distribution Anyone with Java Run Time environment can run it

Answer 151

**File** -\> **Project Structure** -\> **Artifacts** ## Footnote **Build -\> build artifacts**

Answer 152

**Option (press)** + o**ption (hold)** + **down arrow**