Java Concurrency

1. Java Concurrency from docs.oracle.com
Computer users take it for granted that their systems can do more than one thing at a time. They assume that they can continue to work in a word processor, while other applications download files, manage the print queue, and stream audio. Even a single application is often expected to do more than one thing at a time. For example, that streaming audio application must simultaneously read the digital audio off the network, decompress it, manage playback, and update its display. Even the word processor should always be ready to respond to keyboard and mouse events, no matter how busy it is reformatting text or updating the display. Software that can do such things is known as concurrent software.
The Java platform is designed from the ground up to support concurrent programming, with basic concurrency support in the Java programming language and the Java class libraries. Since version 5.0, the Java platform has also included high-level concurrency APIs. This lesson introduces the platform's basic concurrency support and summarizes some of the high-level APIs in the java.util.concurrent packages.

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Gioi thieu Java 8 - Lambda Expressions

Lambda expressions duoc gioi thieu trong Java 8 va duoc coi la mot trong nhung dac diem lon nhat cua Java 8. Lambda expression tang cuong ho tro functional programming, va lam don gian hoa viec viet code.

Syntax

Mot lambda expression duoc dac ta boi cu phap sau −

parameter -> expression body

Following are the important characteristics of a lambda expression −

• Optional type declaration − No need to declare the type of a parameter. The compiler can inference the same from the value of the parameter.
• Optional parenthesis around parameter − No need to declare a single parameter in parenthesis. For multiple parameters, parentheses are required.
• Optional curly braces − No need to use curly braces in expression body if the body contains a single statement.
• Optional return keyword − The compiler automatically returns the value if the body has a single expression to return the value. Curly braces are required to indicate that expression returns a value.

Lambda Expressions Example

Create the following Java program using editor and save in some folder like C:\>JAVA.

Java8Tester.java

public class Java8Tester {
   public static void main(String args[]){
      Java8Tester tester = new Java8Tester();
  
      //with type declaration
      MathOperation addition = (int a, int b) -> a + b;
  
      //with out type declaration
      MathOperation subtraction = (a, b) -> a - b;
  
      //with return statement along with curly braces
      MathOperation multiplication = (int a, int b) -> { return a * b; };
  
      //without return statement and without curly braces
      MathOperation division = (int a, int b) -> a / b;
  
      System.out.println("10 + 5 = " + tester.operate(10, 5, addition));
      System.out.println("10 - 5 = " + tester.operate(10, 5, subtraction));
      System.out.println("10 x 5 = " + tester.operate(10, 5, multiplication));
      System.out.println("10 / 5 = " + tester.operate(10, 5, division));
  
      //without parenthesis
      GreetingService greetService1 = message ->
      System.out.println("Hello " + message);
  
      //with parenthesis
      GreetingService greetService2 = (message) ->
      System.out.println("Hello " + message);
  
      greetService1.sayMessage("Mahesh");
      greetService2.sayMessage("Suresh");
   }
 
   interface MathOperation {
      int operation(int a, int b);
   }
 
   interface GreetingService {
      void sayMessage(String message);
   }
 
   private int operate(int a, int b, MathOperation mathOperation){
      return mathOperation.operation(a, b);
   }
}

Verify the Result

Compile the class using javac compiler as follows −

$javac Java8Tester.java

Now run the Java8Tester as follows −

$java Java8Tester

It should produce the following output −

10 + 5 = 15
10 - 5 = 5
10 x 5 = 50
10 / 5 = 2
Hello Mahesh
Hello Suresh

Following are the important points to be considered in the above example.

• Lambda expressions are used primarily to define inline implementation of a functional interface, i.e., an interface with a single method only. In the above example, we've used various types of lambda expressions to define the operation method of MathOperation interface. Then we have defined the implementation of sayMessage of GreetingService.
• Lambda expression eliminates the need of anonymous class and gives a very simple yet powerful functional programming capability to Java.

Scope

Using lambda expression, you can refer to final variable or effectively final variable (which is assigned only once). Lambda expression throws a compilation error, if a variable is assigned a value the second time.

Scope Example

Create the following Java program using editor and save in some folder like C:\>JAVA.

Java8Tester.java

public class Java8Tester {

   final static String salutation = "Hello! ";
   
   public static void main(String args[]){
      GreetingService greetService1 = message -> 
      System.out.println(salutation + message);
      greetService1.sayMessage("Mahesh");
   }
 
   interface GreetingService {
      void sayMessage(String message);
   }
}

Verify the Result

Compile the class using javac compiler as follows −

$javac Java8Tester.java

Now run the Java8Tester as follows −

$java Java8Tester

It should produce the following output −

Hello! Mahesh

Reference document:

Java SE 8: Lambda Quick Start

java-8-double-colon-operator

From: Java 8 - Lambda Expressions

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Install Android Studio & Java8

Install Java JDK 1.8

• Download jdk-8uversion-linux-x64.tar.gz file from http://www.oracle.com/technetwork/java/javase/downloads/index.html
• Unpack the tarball and install the JDK.
  % tar zxvf jdk-8uversion-linux-x64.tar.gz
• Set up the JAVA_HOME and ANDROID_HOME
  For example, ANDROID_HOME=/home/demo/java/exo-dependencies/Android/AndroidStudio_Latest/SDK
  JAVA_HOME=/home/demo/java/jdk1.8.0_77
  PATH=/usr/local/bin:$PATH:$JAVA_HOME/bin:$M2_HOME/bin:$GRADLE_HOME/bin:$ANDROID_HOME/platform-tools:$ANDROID_HOME/tools

Install Android Studio on Ubuntu

Setting up Android Studio takes just a few clicks.

While the Android Studio download completes, verify which version of the JDK you have: open a command line and type javac -version. If the JDK is not available or the version is lower than 1.8, download the Java SE Development Kit 8.

To install Android Studio on Linux, proceed as follows:

1. Unpack the .zip file you downloaded to an appropriate location for your applications, such as within /usr/local/for your user profile, or /opt/ for shared users.
2. To launch Android Studio, open a terminal, navigate to the android-studio/bin/ directory, and executestudio.sh.
   Tip: Add android-studio/bin/ to your PATH environment variable so you can start Android Studio from any directory.
3. Select whether you want to import previous Android Studio settings or not, then click OK.
4. The Android Studio Setup Wizard guides you though the rest of the setup, which includes downloading Android SDK components that are required for development.

Note: If you are running a 64-bit version of Ubuntu, you need to install some 32-bit libraries with the following command:

sudo apt-get install lib32z1 lib32ncurses5 lib32bz2-1.0 lib32stdc++6

If you are running 64-bit Fedora, the command is:

sudo yum install zlib.i686 ncurses-libs.i686 bzip2-libs.i686

That's it! The following video shows each step of the recommended setup procedure.

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Number literals in Java

Numbers

Numbers in Java can be written in many different forms. Depending on the prefix or suffix we use, we can declare it’s base (binary, hex, octal), and even it’s type (int, long, float).

---

Alterations in the base:

With literal prefixes we can define 4 different numeric bases, and they are: Octal, Hexadecimal, Decimal and Binary.

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Java 2D: Composition Rules

In the standard RGB color model, every color is described by its red, green, and blue components. However, it is also convenient to be able to describe areas of an image that are transparent or partially transparent. When you superimpose an image onto an existing drawing, the transparent pixels do not obscure the pixels under them at all, whereas partially transparent pixels are mixed with the pixels under them. Figure 7-23 shows the effect of overlaying a partially transparent rectangle on an image. You can still see the details of the image shine through from under the rectangle.

Figure 7-23. Overlaying a partially transparent rectangle on an image

 

In the Java 2D API, transparency is described by an alpha channel. Each pixel has, in addition to its red, green, and blue color components, an alpha value between 0 (fully transparent) and 1 (fully opaque). For example, the rectangle in Figure 7-23 was filled with a pale yellow color with 50% transparency:

new Color(0.7F, 0.7F, 0.0F, 0.5F);

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Java 2D: clipping

1. What isclipping

Clipping is the process of confining paint operations to a limited area or shape.

2. Clipping the Drawing Region

Any Shape object can be used as a clipping path that restricts the portion of the drawing area that will be rendered. The clipping path is part of the Graphics2Dcontext; to set the clip attribute, you call Graphics2D.setClip and pass in the Shape that defines the clipping path you want to use. You can shrink the clipping path by calling the clip method and passing in another Shape; the clip is set to the intersection of the current clip and the specified Shape.

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Java 2D: Areas, Strokes, Paint

Areas
An Area object stores and manipulates a resolution-independent description of an enclosed area of 2-dimensional space. Area objects can be transformed and can perform various Constructive Area Geometry (CAG) operations when combined with other Area objects. The CAG operations include area addition, subtraction, intersection, and exclusive or. See the linked method documentation for examples of the various operations.

The Area class implements the Shape interface and provides full support for all of its hit-testing and path iteration facilities, but an Area is more specific than a generalized path in a number of ways..

With the Area class, you can perform boolean operations, such as union, intersection, and subtraction, on any two Shape objects. This technique, often referred to as constructive area geometry, enables you to quickly create complex Shape objects without having to describe each line segment or curve.

Area - Core Java™ 2 Volume II - Advanced Features, Seventh Edition

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Java 2D: Shapes

Here are some of the methods in the Graphics class to draw shapes:

drawLine
drawRectangle
drawRoundRect
draw3DRect
drawPolygon
drawPolyline
drawOval
drawArc

There are also corresponding fill methods. These methods have been in the Graphics class ever since JDK 1.0. The Java 2D API uses a completely different, object-oriented approach. Instead of methods, there are classes:

Line2D
Rectangle2D
RoundRectangle2D
Ellipse2D
Arc2D
QuadCurve2D
CubicCurve2D
GeneralPath

These classes all implement the Shape interface.

Finally, the Point2D class describes a point with an x- and a y-coordinate. Points are useful to define shapes, but they aren't themselves shapes.

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Java 2D: Ví dụ ShapesDemo2D.java

GeneralPath class implements the Shape interface and represents a geometric path constructed from lines, and quadratic and cubic curves. The three constructors in this class can create the GeneralPath object with the default winding rule (WIND_NON_ZERO), the given winding rule (WIND_NON_ZERO or WIND_EVEN_ODD), or the specified initial coordinate capacity. The winding rule specifies how the interior of a path is determined.

public void Paint (Graphics g) {

    Graphics2D g2 = (Graphics2D) g;

    ...

} 

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Java 2D: Coordinate Transformations

Coordinates

The Java 2D™ API maintains two coordinate spaces:

• User space – The space in which graphics primitives are specified
• Device space – The coordinate system of an output device such as a screen, window, or a printer

User space is a device-independent logical coordinate system, the coordinate space that your program uses. All geometries passed into Java 2D rendering routines are specified in user-space coordinates.
When the default transformation from user space to device space is used, the origin of user space is the upper-left corner of the component’s drawing area. The xcoordinate increases to the right, and the y coordinate increases downward, as shown in the following figure. The top-left corner of a window is 0,0. All coordinates are specified using integers, which is usually sufficient. However, some cases require floating point or even double precision which are also supported.

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