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An interface is a reference type, similar to a class, which can be declared by using interface keyword. Interfaces can contain only constants, method signatures, default methods, static methods, and nested types. Method bodies exist only for default methods and static methods. Like abstract classes, Interfaces cannot be instantiated—they can only be implemented by classes or extended by other interfaces. Interface is a common way to achieve full abstraction in Java.

An Intent is a small message passed around the Android system. This message may hold information about our intention to perform a task.

It is basically a passive data structure holding an abstract description of an action to be performed.

The java.util.Map interface represents a mapping between keys and their values. A map cannot contain duplicate keys; and each key can map to at most one value.

Since Map is an interface, then you need to instantiate a concrete implementation of that interface in order to use it; there are several Map implementations, and mostly used are the java.util.HashMap and java.util.TreeMap

Strings (java.lang.String) are pieces of text stored in your program. Strings are not a primitive data type in Java, however, they are very common in Java programs.

In Java, Strings are immutable, meaning that they cannot be changed. (Click here for a more thorough explanation of immutability.)

Default Method introduced in Java 8, allows developers to add new methods to an interface without breaking the existing implementations of this interface. It provides flexibility to allow the interface to define an implementation which will be used as default when a class which implements that interface fails to provide an implementation of that method.

Objects have states and behaviors. Example: A dog has states - color, name, breed as well as behaviors – wagging the tail, barking, eating. An object is an instance of a class.

Class − A class can be defined as a template/blueprint that describes the behavior/state that the object of its type support.

SharedPreferences provide a way to save data to disk in the form of key-value pairs.

Concurrent computing is a form of computing in which several computations are executed concurrently instead of sequentially. Java language is designed to support concurrent programming through the usage of threads. Objects and resources can be accessed by multiple threads; each thread can potentially access any object in the program and the programmer must ensure read and write access to objects is properly synchronized between threads.

Material Design is a comprehensive guide for visual, motion, and interaction design across platforms and devices.

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