They can also quickly transport the app from one platform to the next without constantly compiling the code. Thus it is easier for beginners to learn and use Java in less time. Simultaneously, Java is a rival class-based programming language that is object-oriented. Because Java embraces popular object-oriented programming principles such as heritage, polymorphism, abstraction, and enclosure, the applications are made modular, extensible, and scalable more readily accessible by programmers.
The developers can also benefit from such Java libraries to more effectively incorporate object-oriented design concepts. During the development of mobile apps, the mobile device with the most extensive installation base cannot be overlooked by any developer. But Google suggests the developers of mobile apps write Android apps in Java only. By typing it in Java, developers can further improve the performance and compatibility of the Android apps.
Developers also have the option to write sturdy Android apps in Java in a shorter time, using various tools and libraries. Java dominates other languages in the programming interfaces rich application programming interfaces APIs category. The programmers have the option of creating popular development projects by using a variety of Java APIs without adding any extra code.
Some of these APIs are shared by significant corporations, and others are downloaded by community members. Developers can use APIs to link databases, inputs and outputs, networks, utilities, protection, and XML parsing according to their needs. In general, a Java developer can use Java to write GUI, mobile, and web applications for desktop applications.
The simplicity and versatility of Java make it, in the real sense, a general programming language. Simultaneously, the Java frameworks and programming tools make Java one of the most common languages of the year. Happy learning! Ajay Sarangam 30 Jan Introduction Java is one of the most popular programming languages used by software developers all over the world. Table of contents What is Java?
The object-oriented approach should be employed. It should allow multiple operating systems to run the same program. It should have built-in computer network support. It should be configured to execute code from distant sources safely. Object Orientation The first element, object-oriented OO , applies to a programming and design process. Platform Independence The second feature, platform independence, means that Java written programs have to run on different hardware equally.
Here are some of the reasons why Java is and will remain important in the long run. Mature and Keeps Evolving Java is a sophisticated and stable language for programming. Platform Independent Programmers need to write applications with the use of several devices and platforms. Google Recommends for Android App Development During the development of mobile apps, the mobile device with the most extensive installation base cannot be overlooked by any developer.
This method is used to convert the object to a String representation. Create a new class called Main with a public static void main String[] args. In this method create an instance of the Person class. Add a constructor to your Person class which takes first name, last name and age as parameter. Assign the values to your instance variables. In your main method create at least one object of type Person and use System.
Define methods which allow you to read the values of the instance variables and to set them. These methods are called setter and getter.
Getters should start with get followed by the variable name whereby the first letter of the variable is capitalized. Setter should start with set followed by the variable name whereby the first letter of the variable is capitalized. For example, the variable called firstName would have the getFirstName getter method and the setFirstName String s setter method.
Change your main method so that you create one Person object and use the setter method to change the last name. Create a new object called Address. The Address should allow you to store the address of a person.
Add a new instance variable of this type in the Person object. Also, create a getter and setter for the Address object in the Person object. The following is the expected result after the creation of a Person class and it gets instantiated.
If you use variables of different types Java requires for certain types an explicit conversion. The following gives examples for this conversion. The conversion from string to number is independent from the local settings, e. In this notification a correct number format is "8. The German number "8,20" would result in an error. To convert from a German number, you have to use the NumberFormat class. The challenge is that when the value is, for example, Hence the following complex conversion class.
The Java language defines certain statements with a predefined meaning. The following description lists some of them. The if-then statement is a control flow statement. A block of code is only executed when the test specified by the if part evaluates to true. The optional else block is executed when the if part evaluates to false. The following example code shows a class with two methods.
The first method demonstrates the usage of if-then and the second method demonstrates the usage of if-then-else. The switch statement can be used to handle several alternatives if they are based on the same constant value. Use the equals method to see if two different objects are equal.
Is equal, in case of objects the system checks if the reference variable point to the same object. It will not compare the content of the objects! A for loop is a repetition control structure that allows you to write a block of code which is executed a specific number of times.
The syntax is the following. TIP:For arrays and collections there is also an enhanced for loop available. This loop is covered in the Array description. A while loop is a repetition control structure that allows you to write a block of code which is executed until a specific condition evaluates to false.
The do-while loop is similar to the while loop, with the exception that the condition is checked after the execution. An array is a container object that holds a fixed number of values of a single type. An item in an array is called an element. Every element can be accessed via an index.
The first element in an array is addressed via the 0 index, the second via 1, etc. The String class represents character strings. All string literals, for example, "hello", are implemented as instances of this class. An instance of this class is an object. Strings are immutable, e. Avoid using StringBuffer and prefer StringBuilder. StringBuffer is synchronized and this is almost never useful, it is just slower. For memory efficiency Java uses a String pool.
The string pool allows string literals to be reused. This is possible because strings in Java are immutable. If the same string literal is used in several places in the Java code, only one copy of that string is created.
Whenever a String object is created and gets a string literal assigned the string pool is used. To compare the String objects s1 and s2 , use the s1. Return true if text1 is equal to "Testing". The check is case-sensitive. The check is not case-sensitive. For example, it would also be true for "testing". Define a new StringBuilder which allows to efficiently add "Strings". Return the character at position 1. Note: strings are arrays of chars starting with 0. Look for the String "Test" in String str.
Returns the index of the first occurrence of the specified string. Returns the index of the last occurrence of the specified String "ing" in the String str. Returns true if str ends with String "ing". Returns true if String str starts with String "Test". Splits the character separated myString into an array of strings. Attention: the split string is a regular expression, so if you using special characters which have a meaning in regular expressions, you need to quote them.
In the second example the. The Java programming language supports lambdas as of Java 8. A lambda expression is a block of code with parameters. Lambdas allows to specify a block of code which should be executed later. If a method expects a functional interface as parameter it is possible to pass in the lambda expression instead.
Using lambdas allows to use a condensed syntax compared to other Java programming constructs. For example the Collection interfaces has forEach method which accepts a lambda expression. You can use method references in a lambda expression. Method reference define the method to be called via CalledFrom::method. The Java programming language supports lambdas but not closures.
A lambda is an anonymous function, e. Closures are code fragments or code blocks which can be used without being a method or a class.
This means that a closure can access variables not defined in its parameter list and that it can also be assigned to a variable. A stream from the java. Allow to create a stream of sequence of primitive int-valued elements supporting sequential and parallel aggregate operations. The following example demonstrates how to use streams to filter a list, perform a mapping operation and to create one final result string from it with the reduce method. The following is a larger example for the usage of streams.
With this data model you can use streams and lambdas to filter and search the data as demonstrated in the following example. If you call a method or access a field on an object which is not initialized null you receive a NullPointerException NPE.
The java. Optional class can be used to avoid these NPEs. Optional is a good tool to indicate that a return value may be absent, which can be seen directly in the method signature rather than just mentioning that null may be returned in the JavaDoc. If you want to call a method on an Optional object and check some property you can use the filter method. The filter method takes a predicate as an argument.
If a value is present in the Optional object and it matches the predicate, the filter method returns that value; otherwise, it returns an empty Optional object. The ifPresent method can be used to execute some code on an object if it is present. Assume you have a Todo object and want to call the getId method on it. You can do this via the following code. Via the map method you can transform the object if it is present and via the filter method you can filter for certain values.
To get the real value of an Optional the get method can be used. The System class provides access to the configuratoin of the current working environment. You can access them, via System. Timer and java. TimerTask can be used to schedule tasks. The object which implements TimeTask will then be performed by the Timer based on the given interval. TIP: Improved job scheduling is available via the open source framework quartz.
If you need more assistance we offer Online Training and Onsite training as well as consulting. Introduction to Java programming. This tutorial explains the installation and usage of the Java programming language. It also contains examples for standard programming tasks. Introduction to Java 1. Java virtual machine The Java virtual machine JVM is a software implementation of a computer that executes programs like a real machine. Java Runtime Environment vs.
Development Process with Java Java source files are written as plain text documents. Garbage collector The JVM automatically re-collects the memory which is not referred to by other objects. Classpath The classpath defines where the Java compiler and Java runtime look for.
Installation of Java For the following exercises you need to use at least Java Check installation To run Java programs, you:.
Exercise: Write, compile and run a Java program 3. Write source code The following Java program is developed under Linux using a text editor and the command line.
Compile and run your Java program Open a shell for command line access. Compile your Java source file into a class file with the following command.
By default, the compiler puts each class file in the same directory as its source file. You can specify a separate destination directory with the -d compiler flag.
Using the classpath You can use the classpath to run the program from another place in your directory. Base Java language structure 4.
Class A class is a template that describes the data and behavior associated with an instance of that class. Object An object is an instance of a class. Package Java groups classes into functional packages. Inheritance A class can be derived from another class.
The class from which the subclass is derived is called a superclass. Inheritance allows a class to inherit the behavior and data definitions of another class. Object as superclass Every object in Java implicitly extends the Object class.
Exception handling in Java In Java an exception is an event to indicate an error during the runtime of an application.
In general exceptions are thrown up in the call hierarchy until they get catched. Checked Exceptions Checked Exceptions are explicitly thrown by methods, which might cause the exception or re-thrown by methods in case a thrown Exception is not caught. Runtime Exceptions Runtime Exceptions are Exceptions, which are not explicitly mentioned in the method signature and therefore also do not have to be catched explicitly. Java interfaces 5. What is an interface in Java?
Interfaces can have constants which are always implicitly public, static and final. Implementing Interfaces A class can implement an interface. Evolving interfaces with default methods Before Java 8 evolving interfaces, e.
A class can always override a default method to supply a better behavior. Multiple inheritance of methods If a class implements two interfaces and if these interfaces provide the same default method, Java resolves the correct method for the class by the following rules:. Subtypes win over Supertypes - If a class can inherit a method from two interfaces, and one is a subtype of the other, the class inherts the method from the subtype In all other cases the class needs to implement the default method.
In your implementation you can also call the super method you prefer. Functional interfaces All interfaces that have only one method are called functional interfaces.
Runnable java. Callable java. FileFilter java. Comparator java. Annotations in Java 6. Annotations in Java Annotations provide data about a class that is not part of the programming logic itself. Override methods and the Override annotation If a class extends another class, it inherits the methods from its superclass.
To override a method, you use the same method signature in the source code of the subclass. The following code demonstrates how you can override a method from a superclass. The Deprecated annotations The Deprecated annotation can be used on a field, method, constructor or class and indicates that this element is outdated and should not be used anymore.
Type annotations Java supports that annotations can be placed on any type. Thus, data and code are combined into entities called objects. An object can be thought of as a self-contained bundle of behavior code and state data.
The principle is to separate the things that change from the things that stay the same; often, a change to some data structure requires a corresponding change to the code that operates on that data, or vice versa. This separation into coherent objects provides a more stable foundation for a software system's design. The intent is to make large software projects easier to manage, thus improving quality and reducing the number of failed projects.
Another primary goal of OO programming is to develop more generic objects so that software can become more reusable between projects.
A generic "customer" object, for example, should have roughly the same basic set of behaviors between different software projects, especially when these projects overlap on some fundamental level as they often do in large organizations.
In this sense, software objects can hopefully be seen more as pluggable components, helping the software industry build projects largely from existing and well-tested pieces, thus leading to a massive reduction in development times.
Software reusability has met with mixed practical results, with two main difficulties: the design of truly generic objects is poorly understood, and a methodology for broad communication of reuse opportunities is lacking. Some open source communities want to help ease the reuse problem, by providing authors with ways to disseminate information about generally reusable objects and object libraries.
Platform independence The second characteristic, platform independence, means that programs written in the Java language must run similarly on diverse hardware.
One should be able to write a program once and run it anywhere. This is achieved by most Java compilers by compiling the Java language code "halfway" to bytecode specifically Java bytecode —simplified machine instructions specific to the Java platform. The code is then run on a virtual machine VM , a program written in native code on the host hardware that interprets and executes generic Java bytecode. Further, standardized libraries are provided to allow access to features of the host machines such as graphics, threading and networking in unified ways.
Note that, although there's an explicit compiling stage, at some point, the Java bytecode is interpreted or converted to native machine instructions by the JIT compiler. There are also implementations of Java compilers that compile to native object code, such as GCJ, removing the intermediate bytecode stage, but the output of these compilers can only be run on a single architecture. Sun's license for Java insists that all implementations be "compatible".
This resulted in a legal dispute with Microsoft after Sun claimed that the Microsoft implementation did not support the RMI and JNI interfaces and had added platform-specific features of their own. In response, Microsoft no longer ships Java with Windows, and in recent versions of Windows, Internet Explorer cannot support Java applets without a third-party plug-in. However, Sun and others have made available Java run-time systems at no cost for those and other versions of Windows.
The first implementations of the language used an interpreted virtual machine to achieve portability. More recent JVM implementations produce programs that run significantly faster than before, using multiple techniques.
The first technique is to simply compile directly into native code like a more traditional compiler, skipping bytecodes entirely. This achieves good performance, but at the expense of portability. Another technique, known as just-in-time compilation JIT , translates the Java bytecodes into native code at the time that the program is run which results in a program that executes faster than interpreted code but also incurs compilation overhead during execution. More sophisticated VMs use dynamic recompilation, in which the VM can analyze the behavior of the running program and selectively recompile and optimize critical parts of the program.
Dynamic recompilation can achieve optimizations superior to static compilation because the dynamic compiler can base optimizations on knowledge about the runtime environment and the set of loaded classes. JIT compilation and dynamic recompilation allow Java programs to take advantage of the speed of native code without losing portability.
Portability is a technically difficult goal to achieve, and Java's success at that goal has been mixed. Although it is indeed possible to write programs for the Java platform that behave consistently across many host platforms, the large number of available platforms with small errors or inconsistencies led some to parody Sun's "Write once, run anywhere" slogan as "Write once, debug everywhere". Platform-independent Java is however very successful with server-side applications, such as Web services, servlets , and Enterprise JavaBeans, as well as with Embedded systems based on OSGi, using Embedded Java environments.
Automatic garbage collection One idea behind Java's automatic memory management model is that programmers should be spared the burden of having to perform manual memory management.
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