JAVA특강 / 06. Static

1. Static의 개념 : 모든 인스턴스에서 공통적으로 사용하는 것

2. Static 변수

class Person{
  static int person_count=0;	//공유영역
  public int age=0;	//멤벼변수
  public String name;	//멤버변수
  
  Person(String param_name){	//생성자, 인자
    this.name=param_name;
    person_count++;
    age++;
  }
  public void print_info(){
    System.out.printIn("인구:" + person_count);
    System.out.printIn(name + ":" + age);
  }
}

public static void main(String[] args){
  Person p1 = new Person("홍길동");
  p1.print_info();	//인구:1 홍길동:1
  
  Person p2 = new Person("김길동");
  p2.print_info();	//인구:2 홍길동:1
}

public static void main(String[] args){
  Person p1 = new Person("홍길동");
  p1.print_info();	//인구:1 이름:홍길동
  
  p1.person_count=10;
  
  Person p2 = new Person("김길동");
  p2.print_info();	//인구:11 이름:김길동
}

3. Static 메서드 

class Person{
  static int person_count=0;
  public int age=0;
  
  Person(){
    person_count++;	//1 ->2
  }
  
  public static int get_count(){
    age=1;
    return this.person_count;
  }
}

public static void main(String[] args){
  Person p1 = new Person();
  System.out.printIn(p1.get_count());	//age:1, get_count:1
  
  Person p2 = new Person();
  System.out.printIn(p2.get_count());	//age:1, get_count:2
  
  System.out.printIn(p1.get_count());	//age:1, get_count:2
  System.out.printIn(Person.get_count());	//static인 경우 객체인 Person 사용가능
  						//age:1, get_count:2
}

 

다음 자바 프로그램의 출력값으로 옳은것은?

class Student{
  int id;
  char name;
  static int count=0;
  Student(){
    count++;
  }
}

public class StudentTest{
  public static void main(String[] args){
    Student man1 = new Student();	//1
    Student man2 = new Student();	//2
    Student man3 = new Student();	//3
    Student man4 = new Student();	//4
  }
  System.out.printIn(Student.count);	//4
}