Java Programming Cheat sheet

Transcription

1 Java Programming Cheat sheet compiled by Gregg Roeten 1 compiled by Gregg Roeten... 1 Hello, World... 2 Editing, compiling and executing Built-in data types Declaration and assignment statements Access Modifiers... 4 Class level access modifiers table:... 4 Access Modifiers... 4 Member level - Method, function, interface... 4 Access Modifiers... 4 Non-Access Modifiers... 4 Class declaration... 4 Method... 5 Interface... 5 Constructor... 5 Every class has a constructor. Explicitly or new obj created a constructor is invoked Constructor Overloading - Multiple Constructors for a Java Class... 5 Overloading... 6 Overriding... 6 Create File File.createTempFile() a method of File class... 6 Read File readline method of BufferedReader class Write File write method of BufferedWriter Floating-point numbers Booleans... 7 Comparison operators Parsing command-line arguments Math library Type conversion If and if-else statements Nested if-else statement While and for loops Break statement Do-while loop Switch statement Arrays Compile-time initialization Typical array-processing code Two-dimensional arrays Compile-time initialization Our standard output library Our standard input library Our standard drawing library Our standard audio library Redirection and piping Functions Libraries of functions

2 Our standard random library Our standard statistics library Using an object Creating an object Object-oriented libraries Java's String data type Java's Color data type Our input library Our output library Our picture library Hello, World. Editing, compiling and executing. Built-in data types. Declaration and assignment statements. 2

3 3

4 Access Modifiers Class level access modifiers table: Access Modifiers Same Package Other packages, i.e. World public Y Y nothing Y N Member level - Method, function, interface Access Modifiers Same Class Same Package Subclass Other packages, i.e. World public Y Y Y Y protected Y Y Y N no access modifier Y Y N N private Y N N N Non-Access Modifiers static, final, abstract, synchronized, volatile for threads Class declaration public final class Grclass extends Object implements Serializable, GenericDeclaration, Type, AnnotatedElement 4

5 Method public static int funcname(int a, int b) { // body } public static : modifier. int: return type funcname: function name a, b: formal parameters int a, int b: list of parameters Methods pass Parameters by Value Method overloading same overloading rules apply same name, parameters type diff or # diff Interface Use when expect that unrelated classes would implement your interface. OR You want to specify the behavior of a particular data type, but not concerned about who implements its behavior. /* File name : NameOfInterface.java */ import java.lang.*; public interface NameOfInterface //interface is implicitly abstract. You do // not need to use the abstract keyword //Any number of final, static fields when //Any number of abstract method decls // declaring an interface. { Constructor Every class has a constructor. Explicitly or new obj created a constructor is invoked. public class MyClass { // class that the constructor belongs to. public MyClass() { // constructor, has no return type CAN take parameters // Body of constructor, this one is an empty constructor Constructor Overloading - Multiple Constructors for a Java Class A class can have multiple constructors, as long as their signatures (the parameters they take) are not the same. 5 public class MyClass { private int number = 0; public MyClass() { }

6 Overloading public MyClass(int thenumber) { this.number = thenumber; Single Class AND (number of parameters is different OR parameter types are different ) public void show(string message){ public void show(string message, boolean show){ OK # of arg is diff public void show(integer message){ OK type of arg is diff Overriding public class Animal{ public class Dog extends Animal{ public static void main(string args[]){ Animal a = new Animal(); // Animal reference and object Animal b = new Dog(); // Animal reference but Dog object a.move(); // runs the method in Animal class b.move(); //Runs the method in Dog class Create File File.createTempFile() a method of File class import java.io.file; File.createTempFile() File file = null; File dir = new File("C:/"); file = File.createTempFile("JavaTemp", ".javatemp", dir); Read File readline method of BufferedReader class. import java.io.*; public class Main { public static void main(string[] args) { try { BufferedReader in = new BufferedReader(new FileReader("c:\\filename")); String str; while ((str = in.readline())!= null) { Write File write method of BufferedWriter. import java.io.*; public class Main { public static void main(string[] args) { try { BufferedWriter out = new BufferedWriter(new FileWriter("outfilename")); out.write("astring" Integers. 6

7 Floating-point numbers. Booleans. 7

8 Comparison operators. Parsing command-line arguments. Math library. 8

9 Type conversion. If and if-else statements. Nested if-else statement. 9

10 10

11 While and for loops. Break statement. Do-while loop. Switch statement. 11

12 12

13 Arrays. Compile-time initialization. Typical array-processing code. Two-dimensional arrays. 13

14 Compile-time initialization. Ragged arrays. Our standard output library. 14

15 15

16 Our standard input library. Our standard drawing library. Our standard audio library. 16

17 17

18 Redirection and piping. Functions. 18

19 Libraries of functions. 19

20 Our standard random library. Our standard statistics library. 20

21 21

22 Using an object. Creating an object. Instance variables. Constructors. Instance methods. 22

23 Classes Object-oriented libraries. 23

24 Java's String data type. 24

25 Java's Color data type. Our input library. Our output library. 25

26 Our picture library. 26