learnxinyminutes-docs/java.html.markdown

327 lines
8.0 KiB
Markdown
Raw Normal View History

2013-06-29 17:12:23 +00:00
---
2013-06-30 03:12:03 +00:00
2013-06-29 17:12:23 +00:00
language: java
2013-06-30 03:12:03 +00:00
2013-06-29 17:12:23 +00:00
author: Jake Prather
2013-06-30 03:12:03 +00:00
2013-06-29 17:12:23 +00:00
author_url: http://github.com/JakeHP
2013-06-30 03:12:03 +00:00
2013-06-29 17:12:23 +00:00
---
Java is a general-purpose, concurrent, class-based, object-oriented computer programming language.
2013-06-30 12:50:04 +00:00
[Read more here.](http://docs.oracle.com/javase/tutorial/java/index.html)
2013-06-29 17:12:23 +00:00
```java
2013-06-30 06:13:53 +00:00
// Single-line comments start with //
/*
Multi-line comments look like this.
*/
// Import Packages
import java.util.ArrayList;
import package.path.here;
// Import all "sub-packages"
import java.lang.Math.*;
// Your program's entry point is a function called main
public class Main
{
public static void main (String[] args) throws java.lang.Exception
{
//stuff here
}
}
// Printing, and forcing a new line on next print = println()
System.out.println("Hello World");
System.out.println("Integer: "+10+"Double: "+3.14+ "Boolean: "+true);
// Printing, without forcing a new line on next print = print()
System.out.print("Hello World");
System.out.print("Integer: "+10+"Double: "+3.14+ "Boolean: "+true);
2013-06-29 17:12:23 +00:00
///////////////////////////////////////
// Types
///////////////////////////////////////
2013-06-30 06:16:41 +00:00
// Byte - 8-bit signed two's complement integer
// (-128 <= byte <= 127)
2013-06-30 06:13:53 +00:00
byte foo = 100;
2013-06-30 06:16:41 +00:00
// Short - 16-bit signed two's complement integer
// (-32,768 <= short <= 32,767)
2013-06-30 06:13:53 +00:00
short bar = 10000;
2013-06-30 06:16:41 +00:00
//Integer - 32-bit signed two's complement integer
// (-2,147,483,648 <= int <= 2,147,483,647)
2013-06-30 06:13:53 +00:00
int foo = 1;
2013-06-30 06:16:41 +00:00
//Long - 64-bit signed two's complement integer
// (-9,223,372,036,854,775,808 <= long <= 9,223,372,036,854,775,807)
2013-06-30 06:13:53 +00:00
long bar = 100000L;
2013-06-30 06:16:41 +00:00
// (Java has no unsigned types)
2013-06-30 06:13:53 +00:00
//Float - Single-precision 32-bit IEEE 754 Floating Point
float foo = 234.5f;
//Double - Double-precision 64-bit IEEE 754 Floating Point
double bar = 123.4;
//Boolean - True & False
boolean foo = true;
boolean bar = false;
//Char - A single 16-bit Unicode character
char foo = 'A';
//Make a variable a constant
final int HOURS_I_WORK_PER_WEEK = 9001;
//Strings
String foo = "Hello World!";
// \n is an escaped character that starts a new line
String foo = "Hello World!\nLine2!";
System.out.println(foo);
//Hello World!
//Line2!
//Arrays
//The array size must be decided upon declaration
//The format for declaring an array is follows:
//<datatype> [] <var name> = new <datatype>[<array size>];
int [] array = new int[10];
String [] array = new String[1];
boolean [] array = new boolean[100];
// Indexing an array - Accessing an element
array[0];
// Arrays are mutable; it's just memory!
array[1] = 1;
System.out.println(array[1]); // => 1
array[1] = 2;
System.out.println(array[1]); // => 2
//Others to check out
2013-06-30 06:16:41 +00:00
//ArrayLists - Like arrays except more functionality is offered,
// and the size is mutable
2013-06-30 06:13:53 +00:00
//LinkedLists
//Maps
//HashMaps
2013-06-29 17:12:23 +00:00
///////////////////////////////////////
// Operators
///////////////////////////////////////
2013-06-30 06:13:53 +00:00
int i1 = 1, i2 = 2; // Shorthand for multiple declarations
// Arithmetic is straightforward
i1 + i2; // => 3
i2 - i1; // => 1
i2 * i1; // => 2
i1 / i2; // => 0 (0.5, but truncated towards 0)
// Modulo
11 % 3; // => 2
// Comparison operators
3 == 2; // => 0 (false)
3 != 2; // => 1 (true)
3 > 2; // => 1
3 < 2; // => 0
2 <= 2; // => 1
2 >= 2; // => 1
// Bitwise operators!
~ Unary bitwise complement
<< Signed left shift
>> Signed right shift
>>> Unsigned right shift
& Bitwise AND
^ Bitwise exclusive OR
| Bitwise inclusive OR
// Incrementations
int i=0;
i++; //i = 1. Post-Incrementation
++i; //i = 2. Pre-Incrementation
i--; //i = 1. Post-Decrementation
--i; //i = 0. Pre-Decrementation
2013-06-29 17:12:23 +00:00
///////////////////////////////////////
// Control Structures
///////////////////////////////////////
2013-06-30 06:13:53 +00:00
if (false) {
System.out.println("I never run");
} else if (false) {
System.out.println("I am also never run");
} else {
System.out.println("I print");
}
}
// While loop
int i = 0;
while(i < 100){
System.out.println(i);
//Increment the counter
i++;
}
// Do While Loop
int i = 0;
do{
System.out.println(i);
//Increment the counter
i++;
}while(i < 100);
// For Loop
int i;
//for loop structure => for(<start_statement>;<conditional>;<step>)
for(i=0;i<100;i++){
System.out.println(i);
}
// Switch Case
int month = 8;
2013-06-30 03:54:10 +00:00
String monthString;
switch (month) {
case 1: monthString = "January";
break;
case 2: monthString = "February";
break;
case 3: monthString = "March";
break;
case 4: monthString = "April";
break;
case 5: monthString = "May";
break;
case 6: monthString = "June";
break;
case 7: monthString = "July";
break;
case 8: monthString = "August";
break;
case 9: monthString = "September";
break;
case 10: monthString = "October";
break;
case 11: monthString = "November";
break;
case 12: monthString = "December";
break;
default: monthString = "Invalid month";
break;
}
System.out.println(monthString);
2013-06-29 17:12:23 +00:00
///////////////////////////////////////
// Typecasting
///////////////////////////////////////
2013-06-30 06:13:53 +00:00
// Converting data
//Convert String To Integer
Integer.parseInt("123");//returns an integer version of "123"
//Convert Integer To String
Integer.toString(123);//returns a string version of 123
//For other conversions check out the following classes:
//Double
//Long
//String
// You can also cast java objects, there's a lot of details and
// deals with some more intermediate concepts.
2013-06-30 12:50:04 +00:00
// Feel free to check it out here: http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html
2013-06-30 06:13:53 +00:00
2013-06-29 17:12:23 +00:00
///////////////////////////////////////
2013-06-30 03:52:18 +00:00
// Classes And Functions
2013-06-29 17:12:23 +00:00
///////////////////////////////////////
2013-06-30 06:13:53 +00:00
// Classes Syntax shown below.
// Function declaration syntax:
// <public/private/protected> <return type> <function name>(<args>)
2013-06-30 06:16:41 +00:00
// Here is a quick rundown on access level modifiers (public, private, etc.)
// http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html
2013-06-30 06:13:53 +00:00
public class Bicycle {
// Bicycle's Fields/Variables
public int cadence;
public int gear;
public int speed;
// Constructors are a way of creating classes
// This is a default constructor
public Bicycle(){
gear = 1;
cadence = 50;
startGear = 1;
}
// This is a specified constructor (it contains arguments)
public Bicycle(int startCadence, int startSpeed, int startGear) {
gear = startGear;
cadence = startCadence;
speed = startSpeed;
}
// the Bicycle class has
// four methods
public void setCadence(int newValue) {
cadence = newValue;
}
public void setGear(int newValue) {
gear = newValue;
}
public void applyBrake(int decrement) {
speed -= decrement;
}
public void speedUp(int increment) {
speed += increment;
}
}
//Now..Later in the main / driver of your java program
public class Main
{
public static void main (String[] args) throws java.lang.Exception
{
//Call bicycle's constructor
Bicycle trek = new Bicycle();
//Manipulate your object
trek.speedUp(3);
trek.setCadence(100);
}
}
2013-06-29 17:12:23 +00:00
```
## Further Reading
2013-06-30 03:52:18 +00:00
Other Topics To Research:
2013-06-30 03:54:53 +00:00
2013-06-30 12:50:04 +00:00
* [Inheritance](http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html)
2013-06-30 06:13:53 +00:00
2013-06-30 12:50:04 +00:00
* [Polymorphism](http://docs.oracle.com/javase/tutorial/java/IandI/polymorphism.html)
2013-06-30 06:13:53 +00:00
2013-06-30 12:50:04 +00:00
* [Abstraction](http://docs.oracle.com/javase/tutorial/java/IandI/abstract.html)
2013-06-30 06:13:53 +00:00
2013-06-30 12:50:04 +00:00
* [Exceptions](http://docs.oracle.com/javase/tutorial/essential/exceptions/index.html)
2013-06-30 06:13:53 +00:00
2013-06-30 12:50:04 +00:00
* [Interfaces](http://docs.oracle.com/javase/tutorial/java/IandI/createinterface.html)
* [Generics](http://docs.oracle.com/javase/tutorial/java/generics/index.html)
2013-06-30 06:13:53 +00:00
* The links provided are just to get an understanding of the topic, feel free to google and find specific examples