Wrapper클래스

 

4.  Wrapper클래스

- 기본자료형(int,char,double,..)을 클래스로 포장해 놓은 것

 

- 기본자료형과 관련된 속성과 메소드를 갖는다.

예)
    int    ==> Integer
    char   ==> Character
    long   ==> Long
    double ==> Double
    ...

 

ex>

class  Test05_Wrapper{
    public static void main(String[] args){

 

        Integer in=new Integer("100");
        System.out.println("in:" + in);

 

        //public int intValue()
        //Integer객체를 int형으로 반환
        int n1=in.intValue();
        System.out.println("n1:"+n1);

 

        //가능(jdk1.5이상),오토박싱
        Integer in1=200;

        //가능,언박싱
        int n2=in1;
        System.out.println("in1:"+in1 +",n2:"+n2);

 

        //public static int parseInt(String s)
        //s를 int형으로 바꿔보세요!
        String s="300";
        int n3=Integer.parseInt(s);
        System.out.println("n3:" + n3);

 

        //public static String toBinaryString(int i)
        String s1=Integer.toBinaryString(100);
        System.out.println(100+"을 2진수로 표현하면:" + s1);

 

        //public static double parseDouble(String s)
        String s2="123.34";
        double d=Double.parseDouble(s2);
        System.out.println("d:"+d);

 

    }
}

 

class Test06_Character{
    public static void main(String[] args){

 

        String str="Hello World 2012";
        int letter=0,digit=0,space=0;

        for(int i=0;i<str.length();i++){
            char ch=str.charAt(i);

 

            //public static boolean isLetter(char ch)
            //ch가 문자면 true
            if(Character.isLetter(ch)){
                letter++;
            }

 

            //ch가 숫자면 true
            if(Character.isDigit(ch)){
                digit++;
            }

 

            //ch가 공백이면 true
            if(Character.isWhitespace(ch)){
                space++;
            }
        }

        System.out.println("문자갯수:"+letter);
        System.out.println("숫자갯수:"+digit);
        System.out.println("공백갯수:"+space);
    }
}

 

import java.util.Random;
class Test07_Random{
    public static void main(String[] args){

 

        //public static double random()
        //        :0.0~1.0사이
        for(int i=0;i<10;i++){
            //1부터 10사이의 난수 얻어오기
            int a= (int)(Math.random()*10)+1;
            System.out.print(a+" ");
        }

 

        System.out.println();

 

        Random rnd=new Random();
        for(int i=0;i<10;i++){
            //public int nextInt()
            int b=rnd.nextInt(10);
            System.out.print(b+" ");
        }

    }
}