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When we create any View in layout, we can use the android:onClick attribute to reference a method in the associated activity or fragment to handle the click events. XML Layout <Button android:id="@+id/button" ... // onClick should reference the method in your activity or fra...

You can as well access other interface methods from within your default method. public interface Summable { int getA(); int getB(); default int calculateSum() { return getA() + getB(); } } public class Sum implements Summable { @Override public int get...

Java SE 7 Java 7 introduced the Diamond1 to remove some boiler-plate around generic class instantiation. With Java 7+ you can write: List<String> list = new LinkedList<>(); Where you had to write in previous versions, this: List<String> list = new LinkedList<String>()...

It is helpful to filter the logcat output because there are many messages which are not of interest. To filter the output, open the "Android Monitor" and click on the drop down on the top-right and select Edit Filter Configuration Now you can add custom filters to show messages which ar...

Once the SDK installed, you can open the AVD Manager from the command line using android avd. You can also access AVD Manager from Android studio using Tools > Android > AVD Manager or by clicking on the AVD Manager icon in the toolbar which is the second in the screenshot below.

The AppCompat support library provides themes to build apps with the Material Design specification. A theme with a parent of Theme.AppCompat is also required for an Activity to extend AppCompatActivity. The first step is to customize your theme’s color palette to automatically colorize your app. I...

Using BufferedReader: System.out.println("Please type your name and press Enter."); BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); try { String name = reader.readLine(); System.out.println("Hello, " + name + "!"); } catch(I...

The String type provides two methods for converting strings between upper case and lower case: toUpperCase to convert all characters to upper case toLowerCase to convert all characters to lower case These methods both return the converted strings as new String instances: the original String o...

To check whether a particular String a is being contained in a String b or not, we can use the method String.contains() with the following syntax: b.contains(a); // Return true if a is contained in b, false otherwise The String.contains() method can be used to verify if a CharSequence can be fou...

In order to get the length of a String object, call the length() method on it. The length is equal to the number of UTF-16 code units (chars) in the string. String str = "Hello, World!"; System.out.println(str.length()); // Prints out 13 Live Demo on Ideone A char in a String is UTF...

By using startActivityForResult(Intent intent, int requestCode) you can start another Activity and then receive a result from that Activity in the onActivityResult(int requestCode, int resultCode, Intent data) method. The result will be returned as an Intent. An intent can contain data via a Bundle ...

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...

You can get the value of other primitive data types as a String using one the String class's valueOf methods. For example: int i = 42; String string = String.valueOf(i); //string now equals "42”. This method is also overloaded for other datatypes, such as float, double, boolean, and ...

Maps provide methods which let you access the keys, values, or key-value pairs of the map as collections. You can iterate through these collections. Given the following map for example: Map<String, Integer> repMap = new HashMap<>(); repMap.put("Jon Skeet", 927_654); repMap.p...

String str = "My String"; System.out.println(str.charAt(0)); // "M" System.out.println(str.charAt(1)); // "y" System.out.println(str.charAt(2)); // " " System.out.println(str.charAt(str.length-1)); // Last character "g" To get the nth charac...

Arrays are objects which provide space to store up to its size of elements of specified type. An array's size can not be modified after the array is created. int[] arr1 = new int[0]; int[] arr2 = new int[2]; int[] arr3 = new int[]{1, 2, 3, 4}; int[] arr4 = {1, 2, 3, 4, 5, 6, 7}; int len1 = ar...

A primitive data type such as int holds values directly into the variable that is using it, meanwhile a variable that was declared using Integer holds a reference to the value. According to java API: "The Integer class wraps a value of the primitive type int in an object. An object of type Int...

A short is a 16-bit signed integer. It has a minimum value of -215 (-32,768), and a maximum value of 215 ‑1 (32,767) short example = -48; short myShort = 987; short anotherShort = 17; short addedShorts = (short) (myShort + anotherShort); // 1,004 short subtractedShorts = (short) (myShort - an...

By default, long is a 64-bit signed integer (in Java 8, it can be either signed or unsigned). Signed, it can store a minimum value of -263, and a maximum value of 263 - 1, and unsigned it can store a minimum value of 0 and a maximum value of 264 - 1 long example = -42; long myLong = 284; long ano...

A boolean can store one of two values, either true or false boolean foo = true; System.out.println("foo = " + foo); // foo = true boolean bar = false; System.out.println("bar = " + bar); // bar = false boolean notFoo = !foo; System.out.prin...