krixstin/design-patterns

singleton pattern and visitor pattern in java & js implemented

design-patterns

singleton pattern and visitor pattern in java & js implemented

Singleton Pattern

public class SingleObject {

	private static SingleObject instance = new SingleObject();
  
	// PRIVATE: can't create "new" object
	private SingleObject() {
	}

	// Get the only object available
	public static SingleObject getInstance() {
		return instance;
	}

	public void showMessage() {
		System.out.println("Hello World!");
	}
}

✔️ SingleObject object = SingleObject.getInstance();

❌ SingleObject object = new SingleObject();

Problems/Solutions

Not safe in Multi-Thread Environment:

• loop can be excuted multiple times at the same moment (조건문이 동시에 두번 돌 수 있음)

• shared value can't be maintained well-> use synchronized key word

  public synchronized static void print(String input) {
  		count++;
  		System.out.println(input + "count : "+ count);
  	}
  

Interface can't use static methods

Visitor Pattern

Without chaing the classes of the elements on which it operates, it lets you define a new operations

Source

https://www.tutorialspoint.com/design_pattern/design_pattern_quick_guide.htm