Java Interfaces vs. Abstract Classes: Differences and Implementation, A Must-Know for Beginners
This article explains the differences and core usages between Java interfaces and abstract classes. An interface is a special reference type declared with the `interface` keyword, containing only abstract methods (before Java 8) and constants. It specifies class behavior, implemented by classes using `implements`, supports multiple implementations, cannot be instantiated, and is used to define "what can be done" (e.g., `Flyable` specifies flying behavior). An abstract class is declared with `abstract`, containing abstract methods, concrete methods, and member variables. It serves as a class template, extended by subclasses via `extends` (single inheritance required), and can be instantiated through subclass implementation of abstract methods. It defines "what something is" (e.g., `Animal` defines animal attributes and common methods). Core differences: Interfaces specify behavior, support multiple implementations, and only contain abstract methods/constants; abstract classes define templates, use single inheritance, and can include concrete implementations. Selection suggestions: Use interfaces for behavior specification or multi-implementation scenarios, and abstract classes for class templates or single-inheritance scenarios. Neither can be directly instantiated; abstract class abstract methods must be implemented by subclasses, while interface methods are implicitly `public abstract`. Summary: Interfaces define "what can be done" focusing on behavior, abstract classes define "what something is" focusing on templates. Choose based on specific scenarios.
Read MoreJava For Loop: Simple Implementation for Repeated Operations, A Must-Learn for Beginners
This article introduces the relevant knowledge of for loops in Java. First, it points out that when code needs to be executed repeatedly in programming, loop structures can simplify operations and avoid tedious repetitions. The for loop is the most basic and commonly used loop, suitable for scenarios with a known number of iterations. Its syntax consists of three parts: initialization, condition judgment, and iteration update, which control the execution of the loop through these three parts. Taking printing numbers from 1 to 5 as an example, the article demonstrates the execution process of a for loop: initialize i=1, the condition is i<=5, and iterate with i++. The loop body prints the current number, and the loop ends when i=6, where the condition is no longer met. Classic applications are also listed, such as calculating the sum from 1 to 100 (sum via accumulation) and finding the factorial of 5 (factorial via multiplication). Finally, it emphasizes the key to avoiding infinite loops: ensuring correct condition judgment and iteration updates to prevent the loop variable from not being updated or the condition from always being true. Mastering the for loop enables efficient handling of repeated operations and lays the foundation for learning more complex loops in the future.
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