Comparisons

Java 常見類別與概念的差異比較表。

ArrayList vs Vector

Feature	ArrayList	Vector
Thread-Safety	Not synchronized by default	Synchronized by default
Performance	More efficient, better for single-threaded applications	Slower due to synchronization, better for multi-threaded applications
Growth Rate	Increases size by a certain factor when needed (usually 50% or doubles)	Increases size by a certain factor when needed (usually doubles), growth rate can be specified
Legacy	Part of the Java Collections Framework, recommended choice for general-purpose scenarios	Part of the original Java Collection classes, considered a legacy class

Comparable vs Comparator

Aspect	Comparable (I)	Comparator (I)
Purpose	Allows objects to define their natural ordering	Provides a separate class to define custom sorting order
Interface Method	`int compareTo(T o)`	`int compare(T o1, T o2)`
Sorting Order	Objects are sorted in their natural order	Custom sorting order can be defined
Sortings	Objects can have `only one natural sorting order`	Multiple comparators can be defined for different sorting orders
Implementation	Implemented by the class of the objects being compared	Implemented by a separate class
Usage	Implicitly used by sorting methods (e.g., `Collections.sort()`)	Explicitly passed to sorting methods
Multiple Sorting	To change sorting order, modify the object’s `compareTo()` method	To change sorting order, create and use different comparators
Example	Sorting a list of strings in lexicographic order	Sorting a list of custom objects based on specific attributes
	affects the original class	doesn’t affect the original class
	可比較的	比較器

Comparable
- Use Case : 當你想要默認排序一個類的實例時，比如字典順序、數字大小等，並且排序邏輯在大多數情況下不會改變。
Comparator
- Use Case : 當你想要根據不同的屬性或條件進行排序，或者不希望修改類的 compareTo 方法時。

Callable vs Runnable

Features	Callable	Runnable
Return value	Can return value	No return value
Exception handling	Can throw checked exceptions	Cannot throw checked exceptions
Method signature	V call() throws Exception	void run()
Used in	Future	Thread

StringBuffer vs StringBuilder

Key	StringBuffer	StringBuilder
版本	Java 1	Java 5
同步	Yes	No
效能	Thread-Safe, Slow	Not Thread-Safe, Faster than StringBuffer
儲存位置	Heap	Heap

StringBuffer :
- 沒有 override equals，Object equals 為 == 比較記憶體位址
- StringBuffer 字串與 String 字串比較無意義，Object equals 前提是同類型物件

Lock vs Synchronized

Synchronized blocks must be contained within a single method. lock.lock() and lock.unlock() can be called from different methods.
lock.lock() and lock.unlock() provides the same visibility and happens before guarantees as entering and exiting a synchronized block
Synchronized blocks are always reentrant. Lock could decide not to be.
Synchronized blocks do not guarantee fairness. Locks can.

	`Lock`	`Synchronized`
Across Method	⭕	❌
try to acquire lock	⭕	❌
Fair lock management	⭕	❌
List of waiting threads	⭕	❌

Release of lock in exceptions

Lock

// Situation 1
lock.lock();
doSomethingNifty(); // Throws exception
lock.unlock(); // Oh no, we never release the lock!

// Situation 2
try {
    lock.lock();
} finally {
    lock.unlock(); // need write unlock() in finally
}

Synchronized

When an exception occurs from within a synchronized code block, then JVM smartly releases all the locks acquired by the current thread and will start unwinding the execution stack, till the exception is handled using catch block, otherwise killing the thread.

LinkedList vs Array

	Array	Linked List
儲存結構	儲存相同類型的資料	儲存的Object裡面都包含Data與Pointer(指向下一個Node)
記憶體儲存位置	elements 會存在 sequential memory locations(有順序的記憶體位置)	elements 隨機儲存在記憶體當中某個位置, element指向下一個 element(sequence of the elements)
記憶體空間	需要宣告空間	不受限
存取方式	利用index搜索	必須從頭尋找資料
優點	Search O(1)，較快搜索資料	新增、刪除資料較Array簡單，只要O(1)
	較節省記憶體空間
缺點	新增、刪除資料需要移動整個Array, 花費 O(N)時間在移動舊陣列到新陣列	Search O(N), 沒有index，需要從頭搜尋起
		需要另外記憶體空間儲存 pointer

List.of vs Arrays.asList

Operations	SINGLETONLIST	LIST::OF	ARRAYS::ASLIST	JAVA.UTIL.ARRAYLIST
add	❌	❌	❌	✔️
addAll	❌	❌	❌	✔️
clear	❌	❌	❌	✔️
remove	❌	❌	❌	✔️
removeAll	❗️	❌	❗️	✔️
retainAll	❗️	❌	❗️	✔️
replaceAll	❌	❌	✔️	✔️
set	❌	❌	✔️	✔️
sort	✔️	❌	✔️	✔️
remove on iterator	❌	❌	❌	✔️
set on list-iterator	❌	❌	✔️	✔️

Java Basics