Tutorial by Examples: b

class TrivialClass {} A class consists at a minimum of the class keyword, a name, and a body, which might be empty. You instantiate a class with the new operator. TrivialClass tc = new TrivialClass();

In Android Activities and Services, most callbacks are run on the main thread. This makes it simple to update the UI, but running processor- or I/O-heavy tasks on the main thread can cause your UI to pause and become unresponsive (official documentation on what then happens). You can remedy this by...

With this class: class ObjectMemberVsStaticMember { static int staticCounter = 0; int memberCounter = 0; void increment() { staticCounter ++; memberCounter++; } } the following code snippet: final ObjectMemberVsStaticMember o1 = new ObjectMemberVsStati...

If you have many tasks to execute, and all these tasks are not dependent of the result of the precedent ones, you can use Multithreading for your computer to do all this tasks at the same time using more processors if your computer can. This can make your program execution faster if you have some bi...

A Toolbar is a generalization of ActionBar for use within application layouts. While an ActionBar is traditionally part of an Activity's opaque window decor controlled by the framework, a Toolbar may be placed at any arbitrary level of nesting within a view hierarchy. It can be added by performing t...

For basic prototypes or basic command-line behavior, the following loop comes in handy. public class ExampleCli { private static final String CLI_LINE = "example-cli>"; //console like string private static final String CMD_QUIT = "quit"; //string for exit...

In the ActionListener attached to a javax.swing.Timer, you can keep track of the number of times the Timer executed the ActionListener. Once the required number of times is reached, you can use the Timer#stop() method to stop the Timer. Timer timer = new Timer( delay, new ActionListener() { priv...

public interface MyInterface { public void foo(); int bar(); public String TEXT = "Hello"; int ANSWER = 42; public class X { } class Y { } } Interface members always have public visibility, even if the public keyword is omitted. So both foo...

The ArrayIndexOutOfBoundsException is thrown when a non-existing index of an array is being accessed. Arrays are zero-based indexed, so the index of the first element is 0 and the index of the last element is the array capacity minus 1 (i.e. array.length - 1). Therefore, any request for an array e...

Visible to the class, package, and subclass. Let's see an example with the class Test. public class Test{ public int number = 2; public Test(){ } } Now let's try to create an instance of the class. In this example, we can access number because it is public. public class Ot...

private visibility allows a variable to only be accessed by its class. They are often used in conjunction with public getters and setters. class SomeClass { private int variable; public int getVariable() { return variable; } public void setVariable(int variable) { ...

With no modifier, the default is package visibility. From the Java Documentation, "[package visibility] indicates whether classes in the same package as the class (regardless of their parentage) have access to the member." In this example from javax.swing, package javax.swing; public abs...

Protected visibility causes means that this member is visible to its package, along with any of its subclasses. As an example: package com.stackexchange.docs; public class MyClass{ protected int variable; //This is the variable that we are trying to access public MyClass(){ var...

As you use generic types with utility classes, you may often find that number types aren't very helpful when specified as the object types, as they aren't equal to their primitive counterparts. List<Integer> ints = new ArrayList<Integer>(); Java SE 7 List<Integer> ints = new A...

String s = "this is an example"; String a = s.substring(11); // a will hold the string starting at character 11 until the end ("example") String b = s.substring(5, 10); // b will hold the string starting at character 5 and ending right before character 10 ("is an") S...

A Pattern can be compiled with flags, if the regex is used as a literal String, use inline modifiers: Pattern pattern = Pattern.compile("foo.", Pattern.CASE_INSENSITIVE | Pattern.DOTALL); pattern.matcher("FOO\n").matches(); // Is true. /* Had the regex not been compiled case...

Opening with the default browser This example shows how you can open a URL programmatically in the built-in web browser rather than within your application. This allows your app to open up a webpage without the need to include the INTERNET permission in your manifest file. public void onBrowseCli...

Executors accept a java.lang.Runnable which contains (potentially computationally or otherwise long-running or heavy) code to be run in another Thread. Usage would be: Executor exec = anExecutor; exec.execute(new Runnable() { @Override public void run() { //offloaded work, no need t...

If your computation produces some return value which later is required, a simple Runnable task isn't sufficient. For such cases you can use ExecutorService.submit(Callable<T>) which returns a value after execution completes. The Service will return a Future which you can use to retrieve the r...

import javax.xml.bind.annotation.XmlRootElement; @XmlRootElement public class User { private long userID; private String name; // getters and setters } By using the annotation XMLRootElement, we can mark a class as a root element of an XML file. import java.io.File; ...