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Java Programming and Design Examples
https://github.com/denezt/java-coding-examples

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Java Programming and Design Examples

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README 

        
# Java-Sessions

Java Programming and Computational Design

date: 2013-06-01 00:34:15

name: Computer Science 046 | factsheets

---



# Factsheets



**Variables**



Variable_Declaration

Comment

Note



int age = 21;



This declares an integer variable and initializes it to 21.

Recommended



int nextAge = age + 1;

The initial value of a variable can be an expression (as long as age has been previously declared.)

Recommended



String course= "Udacity";

The variable has type  String and is assigned an initial value of "Udacity". 

Recommended



score= 80;

ERROR: the type is required. This statement will not declare a variable. It is an assignment statement which assigns a new value to an existing variable. 

NOT Recommended



int age= "42";

ERROR: You cannot initialize a number with a String.  "42" is a String. See the quotation marks. 

NOT Recommended



int age;

This declares an integer variable without initializing it. It is best to initialize variables when they are created: int age = 0; If you do not know what value you  want yet 

----



Naming Rule

Example



Names must consist of letters, numbers, an underscore, or a dollar sign only.

score_1



Don't use single letter variable name as you do in  mathematics. While it is legal in Java, it is usually not a good idea because it can make programs harder to understand. (you will encounter a couple of exceptions later)

a



WARNING: Names are case sensitive. Note that by convention, variable names start with a lowercase letter

FinalGrade, finalGrade, and FINALGRADE are all different variables



ERROR Names cannot start with a number.

7up



ERROR. You cannot use a reserved word as a name.

int



ERROR: You cannot use special characters such as * or & in names.

m&m



ERROR: Names cannot contain spaces.

final grade



**Number Types**



Type

Range

Size



int (integer)

–2,147,483,648 to 2,147,483,647(~2.14 billion)

4 bytes



short (integer)

-32,768 to 32,767

 2 bytes 



long (integer)

–9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

 8 bytes



byte

-128 to 127

 1 byte 



double(double-precision floating point)

range of about + or - 10^308

 8 bytes 

float(single-precision floating point)

range of about + or - 10^38 & about 7 significant decimal places

 4 bytes 

char

represents a Unicode character

 2 bytes  

boolean

has only 2 possible values: true or false

 1 bit 



Number Literals

Description

Examples



int

An integer has no fractional part and can be positive, negative, or 0.

5,-100,0



double

A number with fractional part

1.7, 1.0, 2.4E5, 3.47E-2



ERROR

Do not use a comma to separate thousands

1,000,000



ERROR

 Do not use a fraction. Use a decimal instead.

 3 1/4 



**Integer Arithmetic**



Expression

Value (when n =2497)

Description



n/10

249

Notice that the answer is an integer with no decimal part.



n % 10

7

 Always the last digit of n



n /100 

24

Again, decimal part is discarded. Removes the last 2 digits.



n % 100

 97 

 The last two digits. 



n % 2

 1 

 If n % 2 is 0 the number is even. Otherwise it is odd. 



**Math Functions**



Method

Return Value



Math.sqrt (n)

Square root of n ( if n is > or = to 0)



Math.pow(a,b)

a^b( if a = 0, b must be >0)



Math.sin(n)

Sine of n where n is in radians



Math.cos(n)

Cosine of n where n is in radians



Math.tan(n)

Tangent of n where n is in radians



Math.round(n)

closest integer to n as a long



Math.ceil(n)

smallest integer > or = to n as a double



Math.floor(n)

largest integer < or = to n as a double



Math.toRadians(n)

Converts n degrees to radians



Math.toDegrees(n)

Converts n radians to degrees



Math.abs(n)

Absolute value of n |n|



Math.max(a,b)

The larger of a and b



Math.min(a,b)

The smaller of a and b



Math.exp(n)

e^n



Math.log(n)

natural log of n



Math.log10(n)

Base 10 log of n



**String Formatting**



Code

In an Example

Type

What It Prints



d

"%4d"

Decimal integer

 123



x

"%x"

Hexadecimal integer

7A



o

"%o"

Octal integer

173



f

"%5.2f"

Fixed floating-point

12.30



e

"%e"

Exponential (very large or small) floating-point

1.23e+1



g

"%3.2g"

General (medium sized) floating-point

12.3



s

"%s"

String

Tax: 



n

"%n" or "\n"

Line end



**Format Flags**



Flag

In an Example

Meaning

What It Prints



-

"%-6d"

Align left

an integer that takes 6 spaces and starts in the first one



0

"%07.2f"

Show leading zeroes

0001.23



+

"%+7.2f"

Show a plus sign for positive numbers

+1.23



(

"%(6.2f"

Enclose negative numbers in parentheses

-1.23 would look like (1.23)



,

"%,10d"

Show decimal separators

12,300



^

"%^s"

convert letters to uppercase

"tax:" would print as "TAX:"



**Strings**



Example_Code_For_String_Methods

Result

Other info



String str = "Java ";
 str = str + "Programming"

str is assigned the value "Java Programming"

The + sign is used to concatenate Strings



String answer = "Total: " + 42;

answer is set to "Total: 42"

Because "Total: " is a string 42 is converted to a string and then the concatenation takes place



String name = "Sara T";
 int len = name.length();

len is set to 6

The number of characters in a string. A space counts as a character



String city = "San Jose"; 
 String sub = city.substring(1, 3);

sub is set to "an"

Takes the substring starting at position 1 and ending before position 3



String city = "San Jose"; 
 String first = city.substring(0, 1);

first is set to "S"

Gets the first character. The substring has length 1 



String city = "San Jose"; 


String sub = city.substring(4);"

sub is set to "Jose"

If you only supply one parameter, the substring consists of all characters from that position until the end of the String



String city = "San Jose"; 
 

String last = city.substring(city.length() - 1);

returns the string containing the last letter in the string ("e") and assigns it to last

str.substring(str.length() - 1) will always give you the last character as a String



String city = "San Jose";


int index = city.indexOf("Jose")



index is set to 4

returns the index where "Jose" starts



String city = "Santa Barbara";


int index = city.lastIndexOf("a")



index is set to 12

returns the index of the last "a" in the string



String cityWithTypo = "Son Jose";


String cityCorrected = cityWithTypo.replace("Son","San");



Changes all ocurrences of "Son" to "San" in cityWithTypo and put the result in cityCorrected

Will also worked the following ("So","Sa");



String sentence = "Joseph is in San Jose";


int index = sentence.indexOf("Jose", 2)

index is set to 17

indexOf returns the index where "Jose" starts. When an index position is supplied as the second argument (2 in this case), search will begin AFTER that index



Common Loop Algorithms

======================



Sum

-------


total = 0

for each item

     total = total + input




Counting Matches

----------------


matches = 0

for each item

    if the item matches

        matches = matches + 1




Finding the Location of the First Match

----------------


found = false

position = 0

while it's not found, and there are more items

    if the item at position matches

        found = true

    else 

        position = position + 1

if the item was found

    its location is position




Maximum

-----------




largest = the first item

for all the items except the first

    if the current item is larger than largest

        replace the value in largest with the current item




Last Update: 21.08.2021