Java Tutorial

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

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

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

In Java, an annotation is a form of syntactic metadata that can be added to Java source code. It provides data about a program that is not part of the program itself. Annotations have no direct effect on the operation of the code they annotate. Classes, methods, variables, parameters and packages are allowed to be … Read more

The Java language provides three operator for performing bitwise shifting on 32 and 64 bit integer values. These are all binary operators with the first operand being the value to be shifted, and the second operand saying how far to shift. The << or left shift operator shifts the value given by the first operand … Read more

This documentation page is for showing details with example about java class constructors and about Object Class Methods which are automatically inherited from the superclass Object of any newly created class. hashCode() method When a Java class overrides the equals method, it should override the hashCode method as well. As defined in the method’s contract: … Read more

While not required, constructors in Java are methods recognized by the compiler to instantiate specific values for the class which may be essential to the role of the object. This topic demonstrates proper usage of Java class constructors. Default Constructor The “default” for constructors is that they do not have any arguments. In case you … Read more

Operators in Java programming language are special symbols that perform specific operations on one, two, or three operands, and then return a result. The Increment/Decrement Operators (++/–) Variables can be incremented or decremented by 1 using the ++ and — operators, respectively. When the ++ and — operators follow variables, they are called post-increment and … Read more

Maps provide methods which let you access the keys, values, or key-value pairs of the map as collections. Iterating through the contents of a Map. You can iterate through these collections. Given the following map for example: Map repMap = new HashMap<>();repMap.put(“Jon Skeet”, 927_654);repMap.put(“BalusC”, 708_826);repMap.put(“Darin Dimitrov”, 715_567); Iterating through map keys: for (String key : … Read more

The list unmodifiable method is used to returns an unmodifiable view of the specified list. The Collections class provides a way to make a list unmodifiable: List ls = new ArrayList();List unmodifiableList = Collections.unmodifiableList(ls); If you want an unmodifiable list with one item you can use: List unmodifiableList = Collections.singletonList(“Only string in the list”); Moving objects around … Read more

A list is an ordered collection of values. In Java, lists are part of the Java Collections Framework. Lists implement the java.util.List interface, which extends java.util.Collection. Sorting a generic list The Collections class offers two standard static methods to sort a list: sort(List list) applicable to lists where T extends Comparable, and sort(List list, Comparator … Read more

The collections framework in java.util provides a number of generic classes for sets of data with functionality that can’t be provided by regular arrays. Collections framework contains interfaces for Collection, with main sub-interfaces List and Set, and mapping collection Map. Collections are the root interface and are being implemented by many other collection frameworks. Removing … Read more

Java enums (declared using the enum keyword) are shorthand syntax for sizable quantities of constants of a single class. Declaring and using a basic enums Enum can be considered to be syntax sugar for a sealed class that is instantiated only a number of times known at compile-time to define a set of constants. A … Read more