J2SE (Core Java) Quick Reference - JAVA Tutorial PDF

www.jntuworld.com J2SE (Core Java) Quick Reference A.R. KISHORE KUMAR www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference covers:...

www.jntuworld.com J2SE (Core Java) Quick Reference A.R. KISHORE KUMAR www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference covers: · Java Buzz Words · Data Types · Control Structures · Arrays · Strings · OOPS in Java · Static Methods · Inner Class · Abstract Class · Interface · Packages · Exceptions · Generic Types · lang Package · util Package · io Package · net Package · Threads · Abstract Window Toolkit · Swings · Applets www.jntuworld.com www.jntuworld.com Contents 1. Introduction to Java 1 · History of Java 1 · Features of Java ( Java Buzz words) 1 · Obtaining Java Environment 2 · Setting up Java Environment 2 2. Programming Structure 3 · Comments 3 · Structure of the Java Program 3 · Escape Sequence 4 · Creating a Source File 4 · Compiling the Source File into a.class file 5 · Executing the Program 6 · The Java Virtual Machine 6 3. Naming Conventions, Data Types and Operators 8 · Naming Conventions 8 · Data Types 8 · Operators 9 4. Control Structures 12 · Java’s Selection Statements 12 · Java’s Iteration Statements 13 · Java’s Jump Statements 15 5. Accepting Input from Keyboard 18 · Accepting a Single Character from the Keyboard 18 · Accepting a String from Keyboard 19 · Accepting an Integer value from Keyboard 19 · Accepting a Float value from Keyboard 19 · Accepting a Double value from Keyboard 19 · Accepting Other Types of Values 19 6. Arrays, Strings & StringBuffer 21 · Arrays 21 · Single Dimensional Arrays 21 · Multi-Dimensional Arrays (2D, 3D, … arrays) 22 · Creating Strings 23 · Strings 23 · StringBuffer 25 7. Introduction to OOPs 27 · Difference between Procedure Oriented Programming and OOP 27 www.jntuworld.com www.jntuworld.com · Features of OOP 27 · Initializing Instance Variables 31 · Constructor 33 · The keyword ‘this’ 35 · Garbage Collection 36 · The finalize () method 36 8. Methods & Inner Class 37 · Methods 37 · Instance Methods 37 · Static Methods 38 · Inner Class 39 9. Inheritance 41 · Inheritance 41 · The keyword super 43 10. Polymorphism 45 · Dynamic Polymorphism 45 o Method Overloading 45 o Method Overriding 46 · Static Polymorphism 47 · The keyword final 47 · Type Casting 47 11. Abstract Class 50 12. Interface 52 · Types of Inheritance 53 13. Packages 55 · Creating Sub Package 57 · Access Specifier 57 14. Exceptions 60 · throws clause 62 · throw clause 62 · Types of Exceptions 63 15. Wrapper Classes 65 · Character Class 65 · Byte Class 66 · Short Class 67 · Integer Class 67 · Float Class 68 · Long Class 68 www.jntuworld.com www.jntuworld.com · Boolean Class 69 · Double Class 69 · Math Class 70 16. Generic Types 71 · Generic Class 71 · Generic Method 72 · Generic Interface 73 17. The Collection Framework 75 · Collection Object 75 · Retrieving elements from Collection 75 · HashSet Class 76 · LinkedHashSet Class 78 · Stack Class 78 · LinkedList Class 79 · ArrayList Class 80 · Vector Class 82 · HashMap Class 83 · Hashtable Class 84 · Arrays Class 85 · StringTokenizer 86 · Calendar 87 · Date 88 18. Streams and Files 90 · Byte Streams 90 · Character or Text Streams 90 · Serialization of Objects 95 · File Class 97 19. Networking in Java 99 · Socket Programming 99 20. Threads 103 · Creating Thread 104 · MultiTasking using Threads 104 · Multiple Threads acting on Single Object 106 · Thread Synchronization or Thread Safe 107 · Thread Class Methods 108 · Deadlock 108 · Thread Communication 110 · ThreadGroup 112 · Thread States (Life-Cycle of a Thread) 114 www.jntuworld.com www.jntuworld.com 21. Abstract Window Toolkit 115 · Creating the Frame 115 · Event Delegation Model 117 · Closing the Frame 117 · Displaying text in the Frame 119 · Drawing in the Frame 120 · Displaying images in the Frame 122 · Component Class Methods 123 · Listeners and Listener Methods 125 · Creating Push Buttons 125 · Checkbox 127 · Radio Button 128 · Choice Menu 130 · List box 131 · Label, TextField, TextArea 133 · Scrollbar Class 134 · Handling Mouse Events 136 · Handling Keyboard Events 138 22. Swings 141 · Creating a Frame 141 · WindowPane 142 · Displaying Text in the Frame 143 · JComponent class Methods 144 · PushButton 145 · Label 146 · Creating Components in Swing 147 · JComboBox Class 149 · JList Class 150 · JTabbedPane 152 · JTable 153 · JMenu Class 155 · Layout Manager 157 o Flow Layout 158 o Border Layout 159 o Card Layout 160 o Grid Layout 161 o GridBag Layout 162 23. Applets 165 · Creating an applet 165 www.jntuworld.com www.jntuworld.com Java – James Gosling James Gosling is a famous Canadian software developer who has been with Sun Microsystems since 1984 and is considered as father of Java programming language. Gosling did the original design of Java and implemented its original compiler and virtual machine. www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference A.R.Kishore Kumar 1. Introduction to Java History of Java: · In 1990, Sun Micro Systems Inc. (US) was conceived a project to develop software for consumer electronic devices that could be controlled by a remote. This project was called Stealth Project but later its name was changed to Green Project. · In January 1991, Project Manager James Gosling and his team members Patrick Naughton, Mike Sheridan, Chris Wrath, and Ed Frank met to discuss about this project. · Gosling thought C and C++ would be used to develop the project. But the problem he faced with them is that they were system dependent languages. The trouble with C and C++ (and most other languages) is that they are designed to be compiled for a specific target and could not be used on various processors, which the electronic devices might use. · James Gosling with his team started developing a new language, which was completely system independent. This language was initially called OAK. Since this name was registered by some other company, later it was changed to Java. · James Gosling and his team members were consuming a lot of coffee while developing this language. Good quality of coffee was supplied from a place called “Java Island’. Hence they fixed the name of the language as Java. The symbol for Java language is cup and saucer. · Sun formally announced Java at Sun World conference in 1995. On January 23rd 1996, JDK1.0 version was released. Features of Java (Java buzz words): · Simple: Learning and practicing java is easy because of resemblance with c and C++. · Object Oriented Programming Language: Unlike C++, Java is purely OOP. · Distributed: Java is designed for use on network; it has an extensive library which works in agreement with TCP/IP. · Secure: Java is designed for use on Internet. Java enables the construction of virus-free, tamper free systems. · Robust (Strong/ Powerful): Java programs will not crash because of its exception handling and its memory management features. · Interpreted: Java programs are compiled to generate the byte code. This byte code can be downloaded and interpreted by the interpreter..class file will have byte code instructions and JVM which contains an interpreter will execute the byte code. · Portable: Java does not have implementation dependent aspects and it yields or gives same result on any machine. · Architectural Neutral Language: Java byte code is not machine dependent, it can run on any machine with any processor and with any OS. · High Performance: Along with interpreter there will be JIT (Just In Time) compiler which enhances the speed of execution. · Multithreaded: Executing different parts of program simultaneously is called multithreading. This is an essential feature to design server side programs. · Dynamic: We can develop programs in Java which dynamically change on Internet (e.g.: Applets). 1 www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference A.R.Kishore Kumar Obtaining the Java Environment: · We can download the JDK (Java Development Kit) including the compiler and runtime engine from Sun at: http://java.sun.com/javase. · Install JDK after downloading, by default JDK will be installed in C:\Program Files\Java\jdk1.5.0_05 (Here jdk1.5.0_05 is JDK’s version) Setting up Java Environment: After installing the JDK, we need to set at least one environment variable in order to able to compile and run Java programs. A PATH environment variable enables the operating system to find the JDK executables when our working directory is not the JDK's binary directory. · Setting environment variables from a command prompt: If we set the variables from a command prompt, they will only hold for that session. To set the PATH from a command prompt: set PATH=C:\Program Files\Java\jdk1.5.0_05\bin;%PATH% · Setting environment variables as system variables: If we set the variables as system variables they will hold continuously. o Right-click on My Computer o Choose Properties o Select the Advanced tab o Click the Environment Variables button at the bottom o In system variables tab, select path (system variable) and click on edit button o A window with variable name- path and its value will be displayed. o Don’t disturb the default path value that is appearing and just append (add) to that path at the end: ;C:\ProgramFiles\Java\ jdk1.5.0_05\bin; o Finally press OK button. 2 www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference A.R.Kishore Kumar 2. Programming Structure Comments: Comments are description about the aim and features of the program. Comments increase readability of a program. Three types of comments are there in Java: · Single line comments: These comments start with // e.g.: // this is comment line · Multi line comments: These comments start with e.g.: · Java documentation comments: These comments start with These comments are useful to create a HTML file called API (application programming Interface) document. This file contains description of all the features of software. Structure of the Java Program: · As all other programming languages, Java also has a structure. · The first line of the C/C++ program contains include statement. For example, is the header file that contains functions, like printf (), scanf () etc. So if we want to use any of these functions, we should include this header file in C/ C++ program. · Similarly in Java first we need to import the required packages. By default java.lang.* is imported. Java has several such packages in its library. A package is a kind of directory that contains a group of related classes and interfaces. A class or interface contains methods. · Since Java is purely an Object Oriented Programming language, we cannot write a Java program without having at least one class or object. So, it is mandatory to write a class in Java program. We should use class keyword for this purpose and then write class name. · In C/C++, program starts executing from main method similarly in Java, program starts executing from main method. The return type of main method is void because program starts executing from main method and it returns nothing. Sample Program: //A Simple Java Program import java.lang.System; import java.lang.String; class Sample { public static void main(String args[]) { System.out.print ("Hello world"); } } · Since Java is purely an Object Oriented Programming language, without creating an object to a class it is not possible to access methods and members of a class. But main method is also a method inside a class, since program execution starts from main method we need to call main method without creating an object. · Static methods are the methods, which can be called and executed without creating objects. Since we want to call main () method without using an object, we should declare main () 3 www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference A.R.Kishore Kumar method as static. JVM calls main () method using its Classname.main () at the time of running the program. · JVM is a program written by Java Soft people (Java development team) and main () is the method written by us. Since, main () method should be available to the JVM, it should be declared as public. If we don’t declare main () method as public, then it doesn’t make itself available to JVM and JVM cannot execute it. · JVM always looks for main () method with String type array as parameter otherwise JVM cannot recognize the main () method, so we must provide String type array as parameter to main () method. · A class code starts with a {and ends with a}. A class or an object contains variables and methods (functions). We can create any number of variables and methods inside the class. This is our first program, so we had written only one method called main (). · Our aim of writing this program is just to display a string “Hello world”. In Java, print () method is used to display something on the monitor. · A method should be called by using objectname.methodname (). So, to call print () method, create an object to PrintStream class then call objectname.print () method. · An alternative is given to create an object to PrintStream Class i.e. System.out. Here, System is the class name and out is a static variable in System class. out is called a field in System class. When we call this field a PrintStream class object will be created internally. So, we can call print() method as: System.out.print (“Hello world”); · println () is also a method belonging to PrintStream class. It throws the cursor to the next line after displaying the result. · In the above Sample program System and String are the classes present in java.lang package. Escape Sequence: Java supports all escape sequence which is supported by C/ C++. A character preceded by a backslash (\) is an escape sequence and has special meaning to the compiler. When an escape sequence is encountered in a print statement, the compiler interprets it accordingly. Escape Sequence Description \t Insert a tab in the text at this point. \b Insert a backspace in the text at this point. \n Insert a newline in the text at this point. \r Insert a carriage return in the text at this point. \f Insert a form feed in the text at this point. \' Insert a single quote character in the text at this point. \" Insert a double quote character in the text at this point. \\ Insert a backslash character in the text at this point. Creating a Source File: · Type the program in a text editor (i.e. Notepad, WordPad, Microsoft Word or Edit Plus). We can launch the Notepad editor from the Start menu by selecting Programs > Accessories > Notepad. In a new document, type the above code (i.e. Sample Program). · Save the program with filename same as Class_name (i.e. Sample.java) in which main method is written. To do this in Notepad, first choose the File > Save menu item. Then, in the Save dialog box: 4 www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference A.R.Kishore Kumar o Using the Save in combo box, specify the folder (directory) where you'll save your file. In this example, the directory is JQR on the D drive. o In the File name text field, type "Sample.java", including the quotation marks. Then the dialog box should look like this: o Now click Save, and exit Notepad. Compiling the Source File into a.class File: · To Compile the Sample.java program go to DOS prompt. We can do this from the Start menu by choosing Run... and then entering cmd. The window should look similar to the following figure. · The prompt shows current directory. To compile Sample.java source file, change current directory to the directory where Sample.java file is located. For example, if source directory is JQR on the D drive, type the following commands at the prompt and press Enter: Now the prompt should change to D:\JQR> · At the prompt, type the following command and press Enter. javac Sample.java 5 www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference A.R.Kishore Kumar · The compiler generates byte code and Sample.class will be created. Executing the Program (Sample.class): · To run the program, enter java followed by the class name created at the time of compilation at the command prompt in the same directory as: java Sample · The program interpreted and the output is displayed. The Java Virtual Machine: Java Virtual Machine (JVM) is the heart of entire Java program execution process. First of all, the.java program is converted into a.class file consisting of byte code instructions by the java compiler at the time of compilation. Remember, this java compiler is outside the JVM. This.class file is given to the JVM. Following figure shows the architecture of Java Virtual Machine. Figure: The internal architecture of the Java virtual machine. In JVM, there is a module (or program) called class loader sub system, which performs the following instructions: · First of all, it loads the.class file into memory. · Then it verifies whether all byte code instructions are proper or not. If it finds any instruction suspicious, the execution is rejected immediately. 6 www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference A.R.Kishore Kumar · If the byte instructions are proper, then it allocates necessary memory to execute the program. This memory is divided into 5 parts, called run time data areas, which contain the data and results while running the program. These areas are as follows: o Method area: Method area is the memory block, which stores the class code, code of the variables and code of the methods in the Java program. (Method means functions written in a class). o Heap: This is the area where objects are created. Whenever JVM loads a class, method and heap areas are immediately created in it. o Java Stacks: Method code is stored on Method area. But while running a method, it needs some more memory to store the data and results. This memory is allotted on Java Stacks. So, Java Stacks are memory area where Java methods are executed. While executing methods, a separate frame will be created in the Java Stack, where the method is executed. JVM uses a separate thread (or process) to execute each method. o PC (Program Counter) registers: These are the registers (memory areas), which contain memory address of the instructions of the methods. If there are 3 methods, 3 PC registers will be used to track the instruction of the methods. o Native Method Stacks: Java methods are executed on Java Stacks. Similarly, native methods (for example C/C++ functions) are executed on Native method stacks. To execute the native methods, generally native method libraries (for example C/C++ header files) are required. These header files are located and connected to JVM by a program, called Native method interface. Execution Engine contains interpreter and JIT compiler which translates the byte code instructions into machine language which are executed by the microprocessor. Hot spot (loops/iterations) is the area in.class file i.e. executed by JIT compiler. JVM will identify the Hot spots in the.class files and it will give it to JIT compiler where the normal instructions and statements of Java program are executed by the Java interpreter. 7 www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference A.R.Kishore Kumar 3. Naming Conventions, Data Types and Operators Naming Conventions: Naming conventions specify the rules to be followed by a Java programmer while writing the names of packages, classes, methods etc. · Package names are written in small letters. e.g.: java.io, java.lang, java.awt etc · Each word of class name and interface name starts with a capital e.g.: Sample, AddTwoNumbers · Method names start with small letters then each word start with a capital e.g.: sum (), sumTwoNumbers (), minValue () · Variable names also follow the same above method rule e.g.: sum, count, totalCount · Constants should be written using all capital letters e.g.: PI, COUNT · Keywords are reserved words and are written in small letters. e.g.: int, short, float, public, void Data Types: The classification of data item is called data type. Java defines eight simple types of data. byte, short, int, long, char, float, double and boolean. These can be put in four groups: · Integer Data Types: These data types store integer numbers Data Type Memory size Range Byte 1 byte -128 to 127 Short 2 bytes -32768 to 32767 Int 4 bytes -2147483648 to 2147483647 Long 8 bytes -9223372036854775808 to 9223372036854775807 e.g.: byte rno = 10; long x = 150L; L means forcing JVM to allot 8 bytes · Float Data Types: These data types handle floating point numbers Data Type Memory size Range Float 4 bytes -3.4e38 to 3.4e38 Double 8 bytes -1.7e308 to 1.7e308 e.g.: float pi = 3.142f; double distance = 1.98e8; · Character Data Type: This data type represents a single character. char data type in java uses two bytes of memory also called Unicode system. Unicode is a specification to include alphabets of all international languages into the character set of java. Data Type Memory size Range Char 2 bytes 0 to 65535 e.g.: char ch = 'x'; · Boolean Data Type: can handle truth values either true or false e.g.:- boolean response = true; 8 www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference A.R.Kishore Kumar Operators: An operator is a symbol that performs an operation. An operator acts on variables called operands. · Arithmetic operators: These operators are used to perform fundamental operations like addition, subtraction, multiplication etc. Operator Meaning Example Result + Addition 3+4 7 - Subtraction 5-7 -2 * Multiplication 5*5 25 / Division (gives quotient) 14 / 7 2 % Modulus (gives remainder) 20 % 7 6 · Assignment operator: This operator (=) is used to store some value into a variable. Simple Assignment Compound Assignment x=x+y x += y x=x–y x -= y x=x*y x *= y x=xy x /= y · Unary operators: As the name indicates unary operator’s act only on one operand. Operator Meaning Example Explanation - Unary minus j = -k;k value is negated and stored into j b value will be incremented by 1 Increment b++; (called as post incrementation) ++ Operator ++b; b value will be incremented by 1 (called as pre incrementation) b value will be decremented by 1 Decrement b--; (called as post decrementation) -- Operator --b; b value will be decremented by 1 (called as pre decrementation) · Relational operators: These operators are used for comparison purpose. Operator Meaning Example == Equal x == 3 != Not equal x != 3 < Less than x Greater than x>3 c) If a value is greater than b and c && and operator System.out.print(“yes”); then only yes is displayed if(a==1 || b==1) If either a value is 1 or b value is 1 || or operator System.out.print(“yes”); then yes is displayed if( !(a==0) ) If a value is not equal to zero then ! not operator System.out.print(“yes”); only yes is displayed 9 www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference A.R.Kishore Kumar · Bitwise operators: These operators act on individual bits (0 and 1) of the operands. They act only on integer data types, i.e. byte, short, long and int. Operator Meaning Explanation & Bitwise AND Multiplies the individual bits of operands | Bitwise OR Adds the individual bits of operands ^ Bitwise XOR Performs Exclusive OR operation > Right shift Shifts the bits of the number towards right a specified number of positions and also preserves the sign bit. >>> Zero fill right shift Shifts the bits of the number towards right a specified number of positions and it stores 0 (Zero) in the sign bit. ~ Bitwise complement Gives the complement form of a given number by changing 0’s as 1’s and vice versa. · Ternary Operator or Conditional Operator (? :): This operator is called ternary because it acts on 3 variables. The syntax for this operator is: Variable = Expression1? Expression2: Expression3; First Expression1 is evaluated. If it is true, then Expression2 value is stored into variable otherwise Expression3 value is stored into the variable. e.g.: max = (a>b) ? a: b; Program 1: Write a program to perform arithmetic operations //Addition of two numbers class AddTwoNumbers { public static void mian(String args[]) { int i=10, j=20; System.out.println("Addition of two numbers is : " + (i+j)); System.out.println("Subtraction of two numbers is : " + (i-j)); System.out.println("Multiplication of two numbers is : " + (i*j)); System.out.println("Quotient after division is : " + (i/j) ); System.out.println("Remainder after division is : " +(i%j) ); } } Output: 10 www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference A.R.Kishore Kumar Program 2: Write a program to perform Bitwise operations //Bitwise Operations class Bits { public static void main(String args[]) { byte x,y; x=10; y=11; System.out.println ("~x="+(~x)); System.out.println ("x & y="+(x&y)); System.out.println ("x | y="+(x|y)); System.out.println ("x ^ y="+(x^y)); System.out.println ("x2="+(x>>2)); System.out.println ("x>>>2="+(x>>>2)); } } Output: 11 www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference A.R.Kishore Kumar 4. Control Statements Control statements are the statements which alter the flow of execution and provide better control to the programmer on the flow of execution. In Java control statements are categorized into selection control statements, iteration control statements and jump control statements. · Java’s Selection Statements: Java supports two selection statements: if and switch. These statements allow us to control the flow of program execution based on condition. o if Statement: if statement performs a task depending on whether a condition is true or false. Syntax: if (condition) statement1; else statement2; Here, each statement may be a single statement or a compound statement enclosed in curly braces (that is, a block). The condition is any expression that returns a boolean value. The else clause is optional. Program 1: Write a program to find biggest of three numbers. //Biggest of three numbers class BiggestNo { public static void main(String args[]) { int a=5,b=7,c=6; if ( a > b && a>c) System.out.println ("a is big"); else if ( b > c) System.out.println ("b is big"); else System.out.println ("c is big"); } } Output: o Switch Statement: When there are several options and we have to choose only one option from the available ones, we can use switch statement. Syntax: switch (expression) { case value1: //statement sequence break; case value2: //statement sequence 12 www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference A.R.Kishore Kumar break; ………….….. case valueN: //statement sequence break; default: //default statement sequence } Here, depending on the value of the expression, a particular corresponding case will be executed. Program 2: Write a program for using the switch statement to execute a particular task depending on color value. //To display a color name depending on color value class ColorDemo { public static void main(String args[]) { char color = ‘r’; switch (color) { case ‘r’: System.out.println (“red”); break; case ‘g’: System.out.println (“green”); break; case ‘b’: System.out.println (“blue”); break; case ‘y’: System.out.println (“yellow”); break; case ‘w’: System.out.println (“white”); break; default: System.out.println (“No Color Selected”); } } } Output: · Java’s Iteration Statements: Java’s iteration statements are for, while and do-while. These statements are used to repeat same set of instructions specified number of times called loops. A loop repeatedly executes the same set of instructions until a termination condition is met. o while Loop: while loop repeats a group of statements as long as condition is true. Once the condition is false, the loop is terminated. In while loop, the condition is tested first; if it is true, then only the statements are executed. while loop is called as entry control loop. Syntax: while (condition) { statements; } 13 www.jntuworld.com www.jntuworld.com J2SE (Core Java) Quick Reference A.R.Kishore Kumar Program 3: Write a program to generate numbers from 1 to 20. //Program to generate numbers from 1 to 20. class Natural { public static void main(String args[]) { int i=1; while (i