1.1 Introduction Flashcards
(14 cards)
- When we say Java is Simple, what do we mean?
Java is considered simple for two main reasons:
1. Simplified Syntax and Design Philosophy
Built on familiar foundations: Java was designed to be as close to C++ as possible to leverage existing programmer knowledge and standard practices
Removed complexity: Java deliberately omits many rarely used, poorly understood, and confusing features from C++ that typically cause more problems than benefits
Accessible learning curve: The language was designed to be programmed easily without requiring extensive esoteric training
2. Small Runtime Footprint
**Compact core: **The basic Java interpreter and class support requires only about 40KB of memory
Minimal standard libraries: Essential standard libraries and thread support add approximately 175KB
Total lightweight package: The entire self-contained microkernel is around 215KB, enabling Java programs to run standalone on small machines
Design Goal
Java’s simplicity was intentional - to create a system that ordinary programmers could use effectively while maintaining the power needed for serious software development, all within a compact footprint suitable for resource-constrained environments.
Why is Java considered an object-oriented programming language?
Java is considered object-oriented because it follows the fundamental principles of object-oriented design and programming.
What is Object-Oriented Programming?
Object-oriented design is a programming technique that focuses primarily on:
- The data (objects) being manipulated
- The interfaces to those objects that define how they interact
Analogy: Like an “object-oriented” carpenter who focuses mainly on the chair being built (the object) and secondarily on the tools used to make it, rather than thinking primarily about the tools themselves.
Java’s Object-Oriented Features
Core OOP Foundation
- Java’s object-oriented facilities are essentially those of C++
- Built on well-established object-oriented principles that were already proven when Java was developed
Key Differences from C++
- Simplified inheritance model: Java replaced C++’s complex multiple inheritance with a simpler concept of interfaces
- Enhanced runtime capabilities: Java provides richer capacity for runtime introspection compared to C++
Comprehensive OOP Support
- Java’s object-oriented features are comparable to those of C++
- All the essential OOP concepts are fully supported and integrated into the language design
Why is Java Considered Distributed?
Java is considered distributed because it was designed with built-in networking capabilities that make distributed computing straightforward:
Built-in Network Protocol Support
- Extensive TCP/IP libraries: Java includes comprehensive libraries for handling network protocols like HTTP and FTP
- Native internet connectivity: These networking capabilities are part of the core language, not external add-ons
Seamless Remote Access
- URL-based object access: Java applications can open and access objects across the network via URLs
- Unified access model: Accessing remote network resources is as simple as accessing files on the local file system
- Transparent networking: Developers can work with distributed resources without dealing with low-level networking complexities
Historical Context & Innovation
- Revolutionary for its time: In 1995, connecting to web servers from languages like C++ or Visual Basic required significant effort and expertise
- Built-in vs. bolt-on: While other languages required external libraries and complex setup, Java made network programming a fundamental feature
- Modern standard: What seems natural today was groundbreaking when Java was introduced
Why is Java considered a “robust” programming language?
Java is considered robust because it’s designed to create reliable programs through multiple layers of error prevention and detection:
1. Multi-Layered Error Detection
- Early checking: Java compiler detects many problems at compile-time that other languages only catch at runtime
- Dynamic runtime checking: Additional safety checks occur while the program is running
- Proactive design: Eliminates error-prone programming situations before they can cause issues
- 2. Memory Safety Through Pointer Model
- No direct pointers: Java eliminates C/C++-style pointers that can corrupt memory
- Automatic memory management: Prevents overwriting memory and data corruption
- Memory protection: The biggest difference from C/C++ - removes the possibility of pointer-related bugs
3. Reliability Focus
- Intended for critical applications: Designed specifically for programs that must be reliable “in a variety of ways”
- Reduces debugging time: Eliminates hours spent chasing memory corruption bugs common in pointer-based languages
- Error prevention: Emphasis on preventing problems rather than just handling them after they occur
Why is Java considered a secure programming language?
Java is considered secure due to its comprehensive security architecture designed for networked environments
Built-in Security Features
Java was designed from the ground up to prevent common attack vectors:
- Stack overflow protection: Prevents overrunning the runtime stack (common worm/virus attack method)
- Memory isolation: Prevents corrupting memory outside its own process space
- File system protection: Controls reading/writing files without proper permissions
- Virus-free construction: Enables building tamper-free systems
Sandbox Security Model
* Isolated execution environment: Untrusted downloaded code runs in a “sandbox” where it cannot impact the host system
* “Bring it on!” philosophy: Originally designed to safely execute any code regardless of source
* Host system protection: Code cannot “escape” from the sandbox to harm the underlying system
Evolution and Challenges
Initial Success: Security bugs were identified and fixed quickly in early versions
Growing Pains:
* Princeton security experts found subtle implementation flaws
* Hackers became skilled at exploiting security architecture weaknesses
* Sun/Oracle struggled to keep pace with necessary bug fixes
Modern Adaptation:
* Digital signatures became required for remote code
* Browser-based Java delivery became obsolete due to security concerns
Competitive Advantage
Java’s comprehensive security model was superior to alternatives like Microsoft’s ActiveX, which relied solely on digital signatures - clearly insufficient given the frequency of crashes and damage from signed applications.
Why is Java considered “architecture-neutral”?
Java is considered architecture-neutral because it can run on any computer architecture without modification.
How Java Achieves Architecture Neutrality
1. Bytecode Generation
* The Java compiler generates architecture-neutral object files (bytecode)
* Bytecode instructions have nothing to do with any particular computer architecture
* These instructions are designed to be:
1. Easy to interpret on any machine
2. Easy to translate into native machine code on the fly
2. Virtual Machine Approach
- Java uses a “virtual machine” concept (not a new idea - previously used by Lisp, Smalltalk, and Pascal)
- The Java Virtual Machine (JVM) serves as an intermediary layer between bytecode and the actual hardware
- Any processor can execute Java code as long as it has the Java runtime system
Performance and Security Benefits
Performance Optimization
- While interpreting virtual machine instructions is slower than native code, Java offers Just-In-Time (JIT) compilation
- JIT translates the most frequently executed bytecode sequences into optimized machine code during runtime
Enhanced Security
- The virtual machine can check the behavior of instruction sequences
- This provides an additional security layer by monitoring code execution
Why is Java considered a “portable” programming language?
Java is considered portable due to several key design decisions that eliminate platform-specific variations:
1. Fixed Data Type Specifications
- Consistent primitive sizes: All primitive data types have fixed, specified sizes across all platforms
- Example: int is always 32-bit in Java, unlike C/C++ where it can be 16-bit, 32-bit, or any compiler-chosen size*
- Eliminates porting headaches: No need to worry about data type size variations between different systems
- Predictable behavior: Arithmetic operations behave identically across all platforms
2. Standardized Data Storage and Transmission
- Fixed binary format: Binary data is stored and transmitted in a consistent format across platforms
- Byte ordering consistency: Eliminates confusion about endianness (byte order) differences
- Unicode string standard: All strings are saved in standard Unicode format, ensuring text consistency
3. Platform-Independent Libraries
- Abstract interfaces: Core libraries define portable interfaces with platform-specific implementations
- Broad compatibility: Works seamlessly with files, regular expressions, XML, dates/times, databases, network connections, threads, etc.
- OS abstraction: Developers can work without worrying about underlying operating system differences
Important Limitation
User Interface challenges: GUI portability remains difficult - creating interfaces that look good across Windows, Mac, and various UNIX systems is still challenging
Multiple UI toolkit replacements: Java’s original UI toolkit was replaced multiple times due to portability issues
Why is Java considered an “interpreted” programming language?
Java is considered interpreted because of how it executes code:
Core Interpretation Mechanism
- Bytecode execution: The Java interpreter can execute Java bytecodes directly on any machine where the interpreter has been installed/ported
- Platform independence: This allows Java programs to run on different systems without recompilation
- Runtime execution: Code is processed at runtime rather than being fully compiled to native machine code beforehand
Development Process Benefits
- Incremental linking: Java uses a more incremental and lightweight linking process compared to traditional compiled languages
- Faster development cycle: This enables a much more rapid and exploratory development process
- Immediate feedback: Developers can test changes quickly without lengthy compilation steps
Historical Context & Reality Check
The interpretation claim was somewhat overstated initially:
- True interpreted languages: Languages like Lisp, Smalltalk, Visual Basic, Python, R, and Scala offer genuine “try something and instantly see results” experiences
- Java’s limitation: For the first 20 years, Java development environments didn’t focus on immediate, interactive programming
- Late addition: Only with Java 9 (2017) did the jshell tool finally provide the rapid, exploratory programming experience that truly interpreted languages had offered all along
Why is Java considered a “high-performance” programming language?
Java achieves high performance through Just-In-Time (JIT) compilation and sophisticated runtime optimizations:
1. Runtime Translation to Machine Code
- Bytecode compilation: Java bytecodes are translated at runtime into native machine code specific to the CPU the application is running on
- On-the-fly optimization: This runtime compilation allows for performance that goes beyond basic interpreted execution
- Adequate baseline: Even interpreted bytecode performance is usually sufficient for most applications
2. Advanced JIT Compiler Optimizations
- Competitive with traditional compilers: Modern JIT compilers perform as well as, and sometimes better than, traditional static compilers
- Runtime profiling: JIT compilers can monitor which code sections are executed frequently and optimize specifically those “hot spots” for maximum speed
- Dynamic optimization: The compiler has access to runtime information that static compilers don’t have
3. Sophisticated Code Optimization Techniques
- Function inlining: JIT compilers can eliminate function call overhead by inlining methods directly into the calling code
- Class loading awareness: The compiler knows exactly which classes are loaded and can make optimization decisions based on the current runtime environment
- Reversible optimizations: If conditions change (e.g., new classes are loaded), the compiler can undo previous optimizations and re-optimize as needed
Evolution of Performance
While early Java versions faced performance criticism, modern JIT compilers have evolved to leverage runtime information for optimizations that static compilers cannot achieve.
Why is Java considered a multithreaded programming language?
Java is considered multithreaded because it was the first mainstream programming language to natively support concurrent programming.
Historical Context & Innovation
- Pioneer in mainstream concurrency: Java was well ahead of its time when most programming languages showed “shocking disregard” for concurrent programming
- Built-in from the start: Multithreading wasn’t added later - it was designed into Java’s core architecture
Original Motivation (1990s)
- Web programming needs: Early web development required handling server response delays
- User interface responsiveness: Prevented UI freezing while waiting for network responses
- Interactive applications: Enabled better real-time behavior in applications
Modern Relevance
- Post-Moore’s Law era: With processor speed improvements ending, we get more cores instead of faster ones
- Resource utilization: Multithreading keeps multiple processors busy simultaneously
- Concurrency necessity: Modern applications require concurrent programming to perform efficiently
Java’s Advantage
- Manageable complexity: While concurrent programming is inherently difficult, Java provides tools and structures that make it more manageable than in other languages
- Better responsiveness: Enables better interactive responsiveness and real-time behavior in applications
Why is Java considered a “dynamic” programming language?
Java is considered dynamic because it was designed to adapt to evolving environments in several key ways:
1. Runtime Adaptability
- Evolving libraries: Libraries can freely add new methods and instance variables without affecting their existing clients
- No breaking changes: Code can be extended and modified without disrupting programs that depend on it
- Seamless updates: The system can grow and change while maintaining compatibility
2. Runtime Type Information (RTTI)
- Easy type discovery: Finding out runtime type information is straightforward in Java
- Runtime inspection: Programs can examine and understand object types while running
- Flexible code behavior: Code can make decisions based on actual runtime types rather than just compile-time types
3. Code Addition to Running Programs
- Live program modification: Code can be added to programs while they’re already running
- Internet-based deployment: Prime example is downloading and executing code from the Internet to run in browsers
- Dynamic loading: New functionality can be introduced without stopping or restarting the application
What are Java applets and how do they work with the Internet?
What are Java Applets?
Java applets are Java programs specifically designed to work on web pages, downloaded as bytecodes from the Internet and executed on users’ local machines
How They Work
* Simple execution: Users only need a Java-enabled web browser to run applets
* No installation required: Applets run directly in the browser without installing additional software
* Always current: Users automatically get the latest version whenever they visit the web page
* Secure: The Java virtual machine provides security protection against hostile code attacks
Web Integration
* Embedded like images: Applets are inserted into web pages similar to how images are embedded
* Dynamic content: Text flows around the applet space, but unlike static images, applets are “alive”
* Interactive capabilities:
Applets can:
React to user commands
* Change their appearance dynamically
* Exchange data between the user’s computer and the server
Revolutionary Impact
At the time of invention, applets provided capabilities that weren’t possible with existing web technologies:
- Direct manipulation: Interactive content that responded to user input (like mouse rotation and zooming)
- Rich interactivity: Far beyond what rudimentary JavaScript and basic HTML could offer
- No HTML canvas: Applets filled the gap before modern web standards existed
Example Use Case
The Jmol applet demonstrated applet power by displaying molecular structures that users could rotate and zoom with their mouse to better understand molecular composition
