싱글톤, 파이널

Singleton

package singleton;
// 단 하나의 객체만 생성하고싶을때 사용
public class Singleton {
	private static Singleton singleton = new Singleton();
	// private : 내부에서 생성자 사용가능
	
	private Singleton() {}
	
	static Singleton getInstance() {
		return singleton;
	}
}

package singleton;

public class Singleton_Ex {
	public static void main(String[] args) {
//		Singleton obj1 = new Singleton();
//		Singleton obj2 = new Singleton();
	
		Singleton obj1 = Singleton.getInstance();
		Singleton obj2 = Singleton.getInstance();
		
		if(obj1 == obj2) {
			System.out.println("같은 Singleton 객체 입니다.");
		}else {
			System.out.println("다른 Singleton 객체 입니다.");
		}
	}
}

Final

package _final;

public class Person {
	final String nation = "Korean";
	final String ssn;
	String name;
	
	Person(String ssn, String name) {
		this.ssn = ssn;
		this.name = name;
	}
}

package _final;

public class Person_Ex {
	public static void main(String[] args) {
		Person p1 = new Person("123456-1234567", "홍길동");
		System.out.println(p1.nation);
		System.out.println(p1.name);
		System.out.println(p1.ssn);
		
//		p1.nation = "ksa";
//		p1.ssn = "1234";
		p1.name = "감자바";
	}
	
	
}

package _final;

public class Earth {
  static final double EARTH_RADIUS = 6400;
  static final double EARTH_AREA = 4 * Math.PI * EARTH_RADIUS;
  
}

package _final;

public class Earth_Ex {
	public static void main(String[] args) {
		
		System.out.println("지구의 반지름 : " + Earth.EARTH_RADIUS + "km");
		System.out.println("지구의 표면젹 : " + Earth.EARTH_AREA + "km");
	}
}