Interview_GC/StringBuilder/JVM/Overloading/Overriding/Abstract/Interface/Generic

✅ Garbage Collection?

Garbage collection

When Java is run on JVM, manage heap
Stop the world, major GC

💡 https://soheeparklee.github.io/posts/JAVA_JVM/#%EF%B8%8F-garbage-collector-1

String Builder 🆚 String Buffer

Difference between stringbuilder and stringbuffer?

같은점: mutation, APIs like append()
⭐️ 참고로, string is immutable
다른점:

• String Builder: synchronization ❌, fast in single thread
  
• String Buffer: synchronization ⭕️, multithread
  

💡 https://soheeparklee.github.io/posts/JAVA_library/#-string-class

✅ Memory in JAVA

How is JVM memory?
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• method area: (class loaded) static, method, final
  
• heap: (runtime) instance, array
  
• JVM stack: (compile) local variable, parameter
  
• PC register: (thread created)
  
• native method stack: not java
  

💡 https://soheeparklee.github.io/posts/JAVA_JVM/#-jvm-runtime-data-area-%EC%A0%80%EC%9E%A5

Overloading 🆚 Overriding

Overloading and Overriding?

✔️ Overloading:

• method name 🟰
  
• parameter ✖️
  
• return type ✖️
  
• when need several
  

✔️ Overriding:

• method name 🟰
  
• parameter 🟰
  
• return type 🟰
  
• need inheritence from parent
  

💡 https://www.geeksforgeeks.org/difference-between-method-overloading-and-method-overriding-in-java/

Abstract class 🆚 Interface

both used for abstraction

✔️ Abstract class

• extends
  
• cannot be instantiated directly, serves as blueprint for other classes
  
• class can inherit from only one abstract class
  
• method, properties can have any access modifier
  
• can have variables
  
• need to have minimum one abstract method
  
  

✔️ Interface

• implements
  
• set of methods a class must implement
  
• class can inherit multiple abstract class
  
• method, properties: public
  
• no variables
  
• inheriting class should override all interface methods
  

💡 https://www.geeksforgeeks.org/difference-between-abstract-class-and-interface-in-java/

✅ Generic

• parameterized types
  
• allow type to be a parameter to method, class, interface
  
• have predefined type
  
• Inside <>, only reference type(class, interface, array) is possible.
  
• To use primitive types, use wrapper
  

✅ Access Modifier

• public
• protected: inherited
• default: same class, same package
• private

https://soheeparklee.github.io/posts/JAVA_accessmodifier/

Vector 🆚 Arraylist?

Vector

Synchronized.
If one thread is working with vector, other thread cannot have vector

ArrayList

Unsynchronized
several thread can work on arraylist

✅ Serialization?

JSON ➡️ Java, visa versa

💡 https://soheeparklee.github.io/posts/l-serialization/