| Types java app |
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| Data Types and Operators |
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| (Primitive Data Types) |
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| (Non-Primitive Data Types) |
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| Control Flow Statements |
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| Conditional Statements |
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| Looping Statements |
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| Branching Statements |
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| Object-Oriented Programming (OOP) |
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| Classes and Objects |
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| Inheritance |
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| Polymorphism |
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| Encapsulation |
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| Abstraction |
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| Exception Handling |
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| Introduction to Exceptions |
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| Collections Framework |
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| Overview of Collections |
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| Commonly Used Collections |
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| Iterators |
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| Java I/O |
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| File Handling |
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| Serialization |
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| Multithreading |
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| Introduction to Threads |
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| Thread Synchronization |
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| GUI Programming with Swing |
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| Introduction to Swing |
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| Event Handling |
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| Advanced Topics |
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| Java Database Connectivity (JDBC) |
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| JAVA CODE |
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Java Basics
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Working with Objects
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Arrays, Conditionals, and Loops
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Creating Classes and Applications in Java
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More About Methods
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Java Applet Basics
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Graphics, Fonts, and Color
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Simple Animation and Threads
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More Animation, Images, and Sound
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Managing Simple Events and Interactivity
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Creating User Interfaces with the awt
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Windows, Networking, and Other Tidbits
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Modifiers, Access Control, and Class Design
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Packages and Interfaces
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Exceptions
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Multithreading
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Streams and I/O
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Using Native Methods and Libraries
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Under the Hood
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Java Programming Tools
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Working with Data Structures in Java
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Advanced Animation and Media
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Fun with Image Filters
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Client/Server Networking in Java
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Emerging Technologies
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appendix A :- Language Summary
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appendix B :- Class Hierarchy Diagrams
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appendix C The Java Class Library
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appendix D Bytecodes Reference
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appendix E java.applet Package Reference
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appendix F java.awt Package Reference
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appendix G java.awt.image Package Reference
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appendix H java.awt.peer Package Reference
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appendix I java.io Package Reference
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appendix J java.lang Package Reference
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appendix K java.net Package Reference
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appendix L java.util Package Reference
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Package
In Java, a package is a way to organize and manage a group of related classes and interfaces. It provides a mechanism for modularizing code and avoiding naming conflicts.
Recall that each Java class has only a single superclass, and it inherits variables and methods from that superclass and all its superclasses. Although single inheritance makes the relationship between classes and the
functionality those classes implement easy to understand and to design, it can also be somewhat restrictive-in particular, when you have similar behavior that needs to be duplicated across different “branches” of the class
hierarchy. Java solves this problem of shared behavior by using the concept of interfaces, which collect method names into one place and then allow you to add those methods as a group to the various classes that need
them. Note that interfaces contain only method names and interfaces (arguments, for example), not actual definitions.
Although a single Java class can have only one superclass (due to single inheritance), that class can also implement any number of interfaces. By implementing an interface, a class provides method implementations
(definitions) for the method names defined by the interface. If two very disparate classes implement the same interface, they can both respond to the same method calls (as defined by that interface), although what each
class actually does in response to those method calls may be very different.
You don’t need to know very much about interfaces right now. You’ll learn more as the book progresses, so if all this is very confusing, don’t panic!
The final new Java concept for today is packages. Packages in Java are a way of grouping together related classes and interfaces in a single library or collection. Packages enable modular groups of classes to be available
only if they are needed and eliminate potential conflicts between class names in different groups of classes.
You’ll learn all about packages, including how to create and use them, in Week 3. For now, there are only a few things you need to know:
The class libraries in the Java Developer’s Kit are contained in a package called java. The classes in the java package are guaranteed to be available in any Java implementation and are the only classes guaranteed
to be available across different implementations. The java package itself contains other packages for classes that define the language, the input and output classes, some basic networking, the window toolkit
functions, and classes that define applets. Classes in other packages (for example, classes in the sun or netscape packages) may be available only in specific implementations.
By default, your Java classes have access to only the classes in java.lang (the base language package inside the java package). To use classes from any other package, you have to either refer to them explicitly
by package name or import them into your source file.
To refer to a class within a package, list all the packages that class is contained in and the class name, all separated by periods (.). For example, take the Color class, which is contained in the awt package (awt
stands for Abstract Windowing Toolkit). The awt package, in turn, is inside the java package. To refer to the Color class in your program, you use the notation java.awt.Color.
Some more examples of packages in Java:
1. Package Declaration: At the beginning of each Java source file, you can declare the package to which the file belongs using the package keyword followed by the package name. This declaration should be the first non-comment statement in the file.
package com.example.myproject;
2.Directory Structure: Packages are mapped to directories in the file system. Each package corresponds to a directory, and the directory structure reflects the package hierarchy.
For example, if you have a package declaration package com.example.myproject;, the corresponding directory structure would look like this:
com
└── example
└── myproject
3 Importing Packages: To use classes or interfaces from another package, you need to import them using the import statement. You can import specific classes/interfaces or the entire package.
import com.example.otherpackage.OtherClass;
4.Access Modifiers: Classes, interfaces, constructors, and methods within a package have access to each other by default if they have default or package-private access (no access modifier specified). Classes/interfaces with public access are accessible from outside the package.
5.Package Visibility: Classes/interfaces with default (package-private) access are only accessible within the same package. This allows for encapsulation and helps in managing access control.
6.JAR Files: When you compile Java source files, the compiler places the generated bytecode (.class files) into directories corresponding to the package structure. You can package these class files along with other resources into a JAR (Java ARchive) file for distribution.
Packages provide a way to organize code into logical units, facilitate code reuse, and help in managing large projects. They are an essential aspect of Java programming, especially in enterprise-level applications.
Some more examples of packages in Java:
1.Creating a Package: You can create your own package by placing your classes in a directory structure that corresponds to the package name. Here’s an example:
// File: com/example/myproject/MyClass.java
package com.example.myproject;
public class MyClass {
public void hello() {
System.out.println("Hello from MyClass!");
}
}
2.Using Classes from Different Packages: Once you have defined classes within packages, you can use them in other classes by importing them.
// File: com/example/otherpackage/AnotherClass.java
package com.example.otherpackage;
import com.example.myproject.MyClass;
public class AnotherClass {
public static void main(String[] args) {
MyClass myObject = new MyClass();
myObject.hello(); // Outputs: Hello from MyClass!
}
}
3.Java Standard Library Packages: Java comes with a vast standard library organized into packages. For example, you might use classes from the java.util package like ArrayList or HashMap.
import java.util.ArrayList;
import java.util.HashMap;
public class MyCollectionExample {
public static void main(String[] args) {
ArrayList<String> list = new ArrayList<>();
list.add("Java");
list.add("is");
list.add("awesome");
System.out.println(list); // Outputs: [Java, is, awesome]
HashMap<Integer, String> map = new HashMap<>();
map.put(1, "One");
map.put(2, "Two");
map.put(3, "Three");
System.out.println(map); // Outputs: {1=One, 2=Two, 3=Three}
}
}
4.Nested Packages: Packages can be nested within each other to create a deeper package hierarchy. For example:
package com.example.myproject.utilities;
public class UtilityClass {
// Methods and fields
}
5.Third-Party Libraries: When you use third-party libraries in your Java projects, they often come packaged in their own packages. You import and use classes from these libraries just like you do with classes from the Java standard library.
