diff --git a/ta_in/java.html.markdown b/ta_in/java.html.markdown deleted file mode 100644 index 35ec57d8..00000000 --- a/ta_in/java.html.markdown +++ /dev/null @@ -1,713 +0,0 @@ ---- -language: java -contributors: - - ["Jake Prather", "http://github.com/JakeHP"] - - ["Jakukyo Friel", "http://weakish.github.io"] - - ["Madison Dickson", "http://github.com/mix3d"] - - ["Simon Morgan", "http://sjm.io/"] - - ["Zachary Ferguson", "http://github.com/zfergus2"] - - ["Cameron Schermerhorn", "http://github.com/cschermerhorn"] -filename: LearnJava.java ---- - -Java is a general-purpose, concurrent, class-based, object-oriented computer -programming language. -[Read more here.](http://docs.oracle.com/javase/tutorial/java/) - -```java -// Single-line comments start with // -/* -Multi-line comments look like this. -*/ -/** -JavaDoc comments look like this. Used to describe the Class or various -attributes of a Class. -*/ - -// Import ArrayList class inside of the java.util package -import java.util.ArrayList; -// Import all classes inside of java.security package -import java.security.*; - -// Each .java file contains one outer-level public class, with the same name as -// the file. -public class LearnJava { - - // In order to run a java program, it must have a main method as an entry point. - public static void main (String[] args) { - - // Use System.out.println() to print lines. - System.out.println("Hello World!"); - System.out.println( - "Integer: " + 10 + - " Double: " + 3.14 + - " Boolean: " + true); - - // To print without a newline, use System.out.print(). - System.out.print("Hello "); - System.out.print("World"); - - // Use System.out.printf() for easy formatted printing. - System.out.printf("pi = %.5f", Math.PI); // => pi = 3.14159 - - /////////////////////////////////////// - // Variables - /////////////////////////////////////// - - /* - * Variable Declaration - */ - // Declare a variable using - int fooInt; - // Declare multiple variables of the same type , , - int fooInt1, fooInt2, fooInt3; - - /* - * Variable Initialization - */ - - // Initialize a variable using = - int fooInt = 1; - // Initialize multiple variables of same type with same value , , = - int fooInt1, fooInt2, fooInt3; - fooInt1 = fooInt2 = fooInt3 = 1; - - /* - * Variable types - */ - // Byte - 8-bit signed two's complement integer - // (-128 <= byte <= 127) - byte fooByte = 100; - - // Short - 16-bit signed two's complement integer - // (-32,768 <= short <= 32,767) - short fooShort = 10000; - - // Integer - 32-bit signed two's complement integer - // (-2,147,483,648 <= int <= 2,147,483,647) - int fooInt = 1; - - // Long - 64-bit signed two's complement integer - // (-9,223,372,036,854,775,808 <= long <= 9,223,372,036,854,775,807) - long fooLong = 100000L; - // L is used to denote that this variable value is of type Long; - // anything without is treated as integer by default. - - // Note: Java has no unsigned types. - - // Float - Single-precision 32-bit IEEE 754 Floating Point - // 2^-149 <= float <= (2-2^-23) * 2^127 - float fooFloat = 234.5f; - // f or F is used to denote that this variable value is of type float; - // otherwise it is treated as double. - - // Double - Double-precision 64-bit IEEE 754 Floating Point - // 2^-1074 <= x <= (2-2^-52) * 2^1023 - double fooDouble = 123.4; - - // Boolean - true & false - boolean fooBoolean = true; - boolean barBoolean = false; - - // Char - A single 16-bit Unicode character - char fooChar = 'A'; - - // final variables can't be reassigned to another object, - final int HOURS_I_WORK_PER_WEEK = 9001; - // but they can be initialized later. - final double E; - E = 2.71828; - - - // BigInteger - Immutable arbitrary-precision integers - // - // BigInteger is a data type that allows programmers to manipulate - // integers longer than 64-bits. Integers are stored as an array of - // of bytes and are manipulated using functions built into BigInteger - // - // BigInteger can be initialized using an array of bytes or a string. - - BigInteger fooBigInteger = new BigDecimal(fooByteArray); - - - // BigDecimal - Immutable, arbitrary-precision signed decimal number - // - // A BigDecimal takes two parts: an arbitrary precision integer - // unscaled value and a 32-bit integer scale - // - // BigDecimal allows the programmer complete control over decimal - // rounding. It is recommended to use BigDecimal with currency values - // and where exact decimal percision is required. - // - // BigDecimal can be initialized with an int, long, double or String - // or by initializing the unscaled value (BigInteger) and scale (int). - - BigDecimal fooBigDecimal = new BigDecimal(fooBigInteger, fooInt); - - - - // Strings - String fooString = "My String Is Here!"; - - // \n is an escaped character that starts a new line - String barString = "Printing on a new line?\nNo Problem!"; - // \t is an escaped character that adds a tab character - String bazString = "Do you want to add a tab?\tNo Problem!"; - System.out.println(fooString); - System.out.println(barString); - System.out.println(bazString); - - // Arrays - // The array size must be decided upon instantiation - // The following formats work for declaring an array - // [] = new []; - // [] = new []; - int[] intArray = new int[10]; - String[] stringArray = new String[1]; - boolean boolArray[] = new boolean[100]; - - // Another way to declare & initialize an array - int[] y = {9000, 1000, 1337}; - String names[] = {"Bob", "John", "Fred", "Juan Pedro"}; - boolean bools[] = new boolean[] {true, false, false}; - - // Indexing an array - Accessing an element - System.out.println("intArray @ 0: " + intArray[0]); - - // Arrays are zero-indexed and mutable. - intArray[1] = 1; - System.out.println("intArray @ 1: " + intArray[1]); // => 1 - - // Others to check out - // ArrayLists - Like arrays except more functionality is offered, and - // the size is mutable. - // LinkedLists - Implementation of doubly-linked list. All of the - // operations perform as could be expected for a - // doubly-linked list. - // Maps - A set of objects that maps keys to values. A map cannot - // contain duplicate keys; each key can map to at most one value. - // HashMaps - This class uses a hashtable to implement the Map - // interface. This allows the execution time of basic - // operations, such as get and insert element, to remain - // constant even for large sets. - - /////////////////////////////////////// - // Operators - /////////////////////////////////////// - System.out.println("\n->Operators"); - - int i1 = 1, i2 = 2; // Shorthand for multiple declarations - - // Arithmetic is straightforward - System.out.println("1+2 = " + (i1 + i2)); // => 3 - System.out.println("2-1 = " + (i2 - i1)); // => 1 - System.out.println("2*1 = " + (i2 * i1)); // => 2 - System.out.println("1/2 = " + (i1 / i2)); // => 0 (0.5 truncated down) - System.out.println("1/2 = " + (i1 / (i2*1.0))); // => 0.5 - - // Modulo - System.out.println("11%3 = "+(11 % 3)); // => 2 - - // Comparison operators - System.out.println("3 == 2? " + (3 == 2)); // => false - System.out.println("3 != 2? " + (3 != 2)); // => true - System.out.println("3 > 2? " + (3 > 2)); // => true - System.out.println("3 < 2? " + (3 < 2)); // => false - System.out.println("2 <= 2? " + (2 <= 2)); // => true - System.out.println("2 >= 2? " + (2 >= 2)); // => true - - // Boolean operators - System.out.println("3 > 2 && 2 > 3? " + ((3 > 2) && (2 > 3))); // => false - System.out.println("3 > 2 || 2 > 3? " + ((3 > 2) || (2 > 3))); // => true - System.out.println("!(3 == 2)? " + (!(3 == 2))); // => true - - // Bitwise operators! - /* - ~ Unary bitwise complement - << Signed left shift - >> Signed/Arithmetic right shift - >>> Unsigned/Logical right shift - & Bitwise AND - ^ Bitwise exclusive OR - | Bitwise inclusive OR - */ - - // Incrementations - int i = 0; - System.out.println("\n->Inc/Dec-rementation"); - // The ++ and -- operators increment and decrement by 1 respectively. - // If they are placed before the variable, they increment then return; - // after the variable they return then increment. - System.out.println(i++); // i = 1, prints 0 (post-increment) - System.out.println(++i); // i = 2, prints 2 (pre-increment) - System.out.println(i--); // i = 1, prints 2 (post-decrement) - System.out.println(--i); // i = 0, prints 0 (pre-decrement) - - /////////////////////////////////////// - // Control Structures - /////////////////////////////////////// - System.out.println("\n->Control Structures"); - - // If statements are c-like - int j = 10; - if (j == 10){ - System.out.println("I get printed"); - } else if (j > 10) { - System.out.println("I don't"); - } else { - System.out.println("I also don't"); - } - - // While loop - int fooWhile = 0; - while(fooWhile < 100) { - System.out.println(fooWhile); - // Increment the counter - // Iterated 100 times, fooWhile 0,1,2...99 - fooWhile++; - } - System.out.println("fooWhile Value: " + fooWhile); - - // Do While Loop - int fooDoWhile = 0; - do { - System.out.println(fooDoWhile); - // Increment the counter - // Iterated 99 times, fooDoWhile 0->99 - fooDoWhile++; - } while(fooDoWhile < 100); - System.out.println("fooDoWhile Value: " + fooDoWhile); - - // For Loop - // for loop structure => for(; ; ) - for (int fooFor = 0; fooFor < 10; fooFor++) { - System.out.println(fooFor); - // Iterated 10 times, fooFor 0->9 - } - System.out.println("fooFor Value: " + fooFor); - - // For Each Loop - // The for loop is also able to iterate over arrays as well as objects - // that implement the Iterable interface. - int[] fooList = {1, 2, 3, 4, 5, 6, 7, 8, 9}; - // for each loop structure => for ( : ) - // reads as: for each element in the iterable - // note: the object type must match the element type of the iterable. - - for (int bar : fooList) { - System.out.println(bar); - //Iterates 9 times and prints 1-9 on new lines - } - - // Switch Case - // A switch works with the byte, short, char, and int data types. - // It also works with enumerated types (discussed in Enum Types), the - // String class, and a few special classes that wrap primitive types: - // Character, Byte, Short, and Integer. - int month = 3; - String monthString; - switch (month) { - case 1: monthString = "January"; - break; - case 2: monthString = "February"; - break; - case 3: monthString = "March"; - break; - default: monthString = "Some other month"; - break; - } - System.out.println("Switch Case Result: " + monthString); - - // Starting in Java 7 and above, switching Strings works like this: - String myAnswer = "maybe"; - switch(myAnswer){ - case "yes": - System.out.println("You answered yes."); - break; - case "no": - System.out.println("You answered no."); - break; - case "maybe": - System.out.println("You answered maybe."); - break; - default: - System.out.println("You answered " + myAnswer); - break; - } - - // Conditional Shorthand - // You can use the '?' operator for quick assignments or logic forks. - // Reads as "If (statement) is true, use , otherwise, use - // " - int foo = 5; - String bar = (foo < 10) ? "A" : "B"; - System.out.println(bar); // Prints A, because the statement is true - - - //////////////////////////////////////// - // Converting Data Types And Typecasting - //////////////////////////////////////// - - // 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 - - // Typecasting - // You can also cast Java objects, there's a lot of details and deals - // with some more intermediate concepts. Feel free to check it out here: - // http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html - - - /////////////////////////////////////// - // Classes And Functions - /////////////////////////////////////// - - System.out.println("\n->Classes & Functions"); - - // (definition of the Bicycle class follows) - - // Use new to instantiate a class - Bicycle trek = new Bicycle(); - - // Call object methods - trek.speedUp(3); // You should always use setter and getter methods - trek.setCadence(100); - - // toString returns this Object's string representation. - System.out.println("trek info: " + trek.toString()); - - // Double Brace Initialization - // The Java Language has no syntax for how to create static Collections - // in an easy way. Usually you end up in the following way: - - private static final Set COUNTRIES = new HashSet(); - static { - validCodes.add("DENMARK"); - validCodes.add("SWEDEN"); - validCodes.add("FINLAND"); - } - - // But there's a nifty way to achieve the same thing in an - // easier way, by using something that is called Double Brace - // Initialization. - - private static final Set COUNTRIES = HashSet() {{ - add("DENMARK"); - add("SWEDEN"); - add("FINLAND"); - }} - - // The first brace is creating a new AnonymousInnerClass and the - // second one declares an instance initializer block. This block - // is called when the anonymous inner class is created. - // This does not only work for Collections, it works for all - // non-final classes. - - } // End main method -} // End LearnJava class - - -// You can include other, non-public outer-level classes in a .java file, -// but it is good practice. Instead split classes into separate files. - - -// Class Declaration Syntax: -// class { -// // data fields, constructors, functions all inside. -// // functions are called as methods in Java. -// } - -class Bicycle { - - // Bicycle's Fields/Variables - public int cadence; // Public: Can be accessed from anywhere - private int speed; // Private: Only accessible from within the class - protected int gear; // Protected: Accessible from the class and subclasses - String name; // default: Only accessible from within this package - - // Constructors are a way of creating classes - // This is a constructor - public Bicycle() { - // You can also call another constructor: - // this(1, 50, 5, "Bontrager"); - gear = 1; - cadence = 50; - speed = 5; - name = "Bontrager"; - } - - // This is a constructor that takes arguments - public Bicycle(int startCadence, int startSpeed, int startGear, - String name) { - this.gear = startGear; - this.cadence = startCadence; - this.speed = startSpeed; - this.name = name; - } - - // Method Syntax: - // () - - // Java classes often implement getters and setters for their fields - - // Method declaration syntax: - // () - public int getCadence() { - return cadence; - } - - // void methods require no return statement - public void setCadence(int newValue) { - cadence = newValue; - } - - public void setGear(int newValue) { - gear = newValue; - } - - public void speedUp(int increment) { - speed += increment; - } - - public void slowDown(int decrement) { - speed -= decrement; - } - - public void setName(String newName) { - name = newName; - } - - public String getName() { - return name; - } - - //Method to display the attribute values of this Object. - @Override // Inherited from the Object class. - public String toString() { - return "gear: " + gear + " cadence: " + cadence + " speed: " + speed + - " name: " + name; - } -} // end class Bicycle - -// PennyFarthing is a subclass of Bicycle -class PennyFarthing extends Bicycle { - // (Penny Farthings are those bicycles with the big front wheel. - // They have no gears.) - - public PennyFarthing(int startCadence, int startSpeed){ - // Call the parent constructor with super - super(startCadence, startSpeed, 0, "PennyFarthing"); - } - - // You should mark a method you're overriding with an @annotation. - // To learn more about what annotations are and their purpose check this - // out: http://docs.oracle.com/javase/tutorial/java/annotations/ - @Override - public void setGear(int gear) { - gear = 0; - } -} - -// Interfaces -// Interface declaration syntax -// interface extends { -// // Constants -// // Method declarations -// } - -// Example - Food: -public interface Edible { - public void eat(); // Any class that implements this interface, must - // implement this method. -} - -public interface Digestible { - public void digest(); -} - - -// We can now create a class that implements both of these interfaces. -public class Fruit implements Edible, Digestible { - - @Override - public void eat() { - // ... - } - - @Override - public void digest() { - // ... - } -} - -// In Java, you can extend only one class, but you can implement many -// interfaces. For example: -public class ExampleClass extends ExampleClassParent implements InterfaceOne, - InterfaceTwo { - - @Override - public void InterfaceOneMethod() { - } - - @Override - public void InterfaceTwoMethod() { - } - -} - -// Abstract Classes - -// Abstract Class declaration syntax -// abstract extends { -// // Constants and variables -// // Method declarations -// } - -// Marking a class as abstract means that it contains abstract methods that must -// be defined in a child class. Similar to interfaces, abstract classes cannot -// be instantiated, but instead must be extended and the abstract methods -// defined. Different from interfaces, abstract classes can contain a mixture of -// concrete and abstract methods. Methods in an interface cannot have a body, -// unless the method is static, and variables are final by default, unlike an -// abstract class. Also abstract classes CAN have the "main" method. - -public abstract class Animal -{ - public abstract void makeSound(); - - // Method can have a body - public void eat() - { - System.out.println("I am an animal and I am Eating."); - // Note: We can access private variable here. - age = 30; - } - - // No need to initialize, however in an interface - // a variable is implicitly final and hence has - // to be initialized. - protected int age; - - public void printAge() - { - System.out.println(age); - } - - // Abstract classes can have main function. - public static void main(String[] args) - { - System.out.println("I am abstract"); - } -} - -class Dog extends Animal -{ - // Note still have to override the abstract methods in the - // abstract class. - @Override - public void makeSound() - { - System.out.println("Bark"); - // age = 30; ==> ERROR! age is private to Animal - } - - // NOTE: You will get an error if you used the - // @Override annotation here, since java doesn't allow - // overriding of static methods. - // What is happening here is called METHOD HIDING. - // Check out this awesome SO post: http://stackoverflow.com/questions/16313649/ - public static void main(String[] args) - { - Dog pluto = new Dog(); - pluto.makeSound(); - pluto.eat(); - pluto.printAge(); - } -} - -// Final Classes - -// Final Class declaration syntax -// final { -// // Constants and variables -// // Method declarations -// } - -// Final classes are classes that cannot be inherited from and are therefore a -// final child. In a way, final classes are the opposite of abstract classes -// because abstract classes must be extended, but final classes cannot be -// extended. -public final class SaberToothedCat extends Animal -{ - // Note still have to override the abstract methods in the - // abstract class. - @Override - public void makeSound() - { - System.out.println("Roar"); - } -} - -// Final Methods -public abstract class Mammal() -{ - // Final Method Syntax: - // final () - - // Final methods, like, final classes cannot be overridden by a child class, - // and are therefore the final implementation of the method. - public final boolean isWarmBlooded() - { - return true; - } -} -``` - -## Further Reading - -The links provided here below are just to get an understanding of the topic, feel free to Google and find specific examples. - -**Official Oracle Guides**: - -* [Java Tutorial Trail from Sun / Oracle](http://docs.oracle.com/javase/tutorial/index.html) - -* [Java Access level modifiers](http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html) - -* [Object-Oriented Programming Concepts](http://docs.oracle.com/javase/tutorial/java/concepts/index.html): - * [Inheritance](http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html) - * [Polymorphism](http://docs.oracle.com/javase/tutorial/java/IandI/polymorphism.html) - * [Abstraction](http://docs.oracle.com/javase/tutorial/java/IandI/abstract.html) - -* [Exceptions](http://docs.oracle.com/javase/tutorial/essential/exceptions/index.html) - -* [Interfaces](http://docs.oracle.com/javase/tutorial/java/IandI/createinterface.html) - -* [Generics](http://docs.oracle.com/javase/tutorial/java/generics/index.html) - -* [Java Code Conventions](http://www.oracle.com/technetwork/java/codeconv-138413.html) - -**Online Practice and Tutorials** - -* [Learneroo.com - Learn Java](http://www.learneroo.com) - -* [Codingbat.com](http://codingbat.com/java) - - -**Books**: - -* [Head First Java](http://www.headfirstlabs.com/books/hfjava/) - -* [Thinking in Java](http://www.mindview.net/Books/TIJ/) - -* [Objects First with Java](http://www.amazon.com/Objects-First-Java-Practical-Introduction/dp/0132492660) - -* [Java The Complete Reference](http://www.amazon.com/gp/product/0071606300)