Method w/ Parameter Description List.of(E e) A generic type that can be a class or interface. Set.of(E e) A generic type that can be a class or interface. Map.of(K k, V v) A key-value pair of generic types that can each be a class or interface. Map.of(Map.Entry<? extends V> entry) A Map.Entry instance where its … Read more
Readers and Writers and their respective subclasses provide simple I/O for text / character-based data. BufferedReader Introduction The BufferedReader class is a wrapper for other Reader classes that serves two main purposes: A BufferedReader provides buffering for the wrapped Reader. This allows an application to read charactersmone at a time without undue I/O overheads. A … Read more
Using preferences Preferences can be used to store user settings that reflect a user’s personal application settings, e.g. their editor font, whether they prefer the application to be started in full-screen mode, whether they checked a “don’t show this again” checkbox and things like that. public class ExitConfirmer { private static boolean confirmExit() { Preferences … Read more
Closing Streams Most streams must be closed when you are done with them, otherwise you could introduce a memory leak or leave a file open. It is important that streams are closed even if an exception is thrown. Version ≥ Java SE 7 try(FileWriter fw = new FileWriter(“outfilename”); BufferedWriter bw = new BufferedWriter(fw); PrintWriter out … Read more
A Java application can accept any number of command line argument. This allows the user to specify configuration information when the application is launched. When an application is launched, the runtime system passes the command line arguments to the application’s main method via an array of String s. Related Article: The Java Command – ‘java’ and ‘javaw’ Parameter Details … Read more
Java.exe is connected to the console while Javaw.exe has no such connection. So while java.exe is running, a command prompt window is automatically opened in which performance and error streams are displayed. … The javaw command is similar to java, except that javaw does not have a console window associated with it. Entry point classes … Read more
The java commands supports a wide range of options: All options start with a single hyphen or minus-sign (-): the GNU/Linux convention of using — for “long” options is not supported. Options must appear before the or the -jar argument to be recognized. Any arguments after them will be treated as arguments to be passed … Read more
Elements from a Stream can be easily collected into a container by using the Stream.collect operation: Collect with toList() and toSet() Elements from a Stream can be easily collected into a container by using theStream.collect operation: System.out.println(Arrays .asList(“apple”, “banana”, “pear”, “kiwi”, “orange”) .stream() .filter(s -> s.contains(“a”)) .collect(Collectors.toList()) ); // prints: [apple, banana, pear, orange] Other … Read more
Java 8 provides classes called IntSummaryStatistics, DoubleSummaryStatistics and LongSummaryStatistics which give a state object for collecting statistics such as count, min, max, sum, and average. Version ≥ Java SE 8 List naturalNumbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); IntSummaryStatistics stats = naturalNumbers.stream() .mapToInt((x) -> x) .summaryStatistics(); System.out.println(stats); Which will result … Read more
Method references make excellent self-documenting code, and using method references with Streams makes complicated processes simple to read and understand. Consider the following code: public interface Ordered { default int getOrder(){ return 0; } } public interface Valued { boolean hasPropertyTwo(); V getValue(); } public interface Thing { boolean hasPropertyOne(); Valued getValuedProperty(); } public List … Read more
A Streams represents a sequence of elements and supports different kind of operations to perform computations upon those elements. With Java 8, Collection interface has two methods to generate a Stream: stream() andparallelStream(). Stream operations are either intermediate or terminal. Intermediate operations return a Stream so multiple intermediate operations can be chained before the Stream … Read more
The Java Console class is be used to get input from console. It provides methods to read texts and passwords. If you read password using Console class, it will not be displayed to the user. The java.io.Console class is attached with system console internally. Reading user input from the console Using BufferedReader: System.out.println(“Please type your … Read more
Reference datatypes in java are those which contains reference/address of dynamically created objects. These are not predefined like primitive data types. Different Reference Types java.lang.ref package provides reference-object classes, which support a limited degree of interaction with the garbage collector. Java has four main different reference types. They are: Strong Reference Weak Reference Soft Reference Phantom … Read more
The idea behind programming to an interface is to base the code primarily on interfaces and only use concrete classes at the time of instantiation. In this context, good code dealing with e.g. Java collections will look somethinglike this (not that the method itself is of any use at all, just illustration): public Set toSet(Collection … Read more
The Liskov Substitution Principle, which provides a lot of details on it. As per the LSP, functions that use references to base classes must be able to use objects of the derived class without knowing it. In simple words, derived classes must be substitutable for the base class. To illustrate the LSP, let’s take an … Read more
package in java is used to group class and interfaces. This helps developer to avoid conflict when there are huge numbers of classes. If we use this package the classes we can create a class/interface with same name in different packages. By using packages we can import the piece of again in another class. There … Read more
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 ofthat method. Basic … Read more
Local Inner Classes are the inner classes that are defined inside a block. Generally, this block is a method body. … These classes have access to the fields of the class enclosing it. Local inner classes are must be instantiated in the block they are defined in. Basic Object Construction and Use in Java Objects come Basic Object Construction and Use in Java in … Read more
There are many differences between method overloading and method overriding in java. A list of differences between method overloading and method overriding are given below: 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 … Read more
Generics are a facility of generic programming that extend Java’s type system to allow a type or method to operate on objects of various types while providing compile-time type safety. In particular, the Java collections framework supports generics to specify the type of objects stored in a collection instance. Related Article: Visibility (controlling access to … Read more