[JAVA 37] 자바 랜덤 / 무작위 ( Random )

■ Random ( 랜덤 )

1. With Random

import java.util.*;
 
class RandomS2{
    Random random = new Random();
 
    void m1(){        // 방법 1. With Random 
        int a = 3;
        int b = random.nextInt(a);    // 0 , 1 , 2 >> 0 ~ ( n-1 )
        System.out.println("b : " + b);
 
        boolean c = random.nextBoolean();
        System.out.println("c : " + c);
    }
 
    public static void main(String[] args){
        RandomS2 rs2 = new RandomS2();
        rs2.m1();
    }
}

2. With Math

import java.util.*;
 
class RandomS2{
    Random random = new Random();
 
    void m1(){        // 방법 2. With Math 
        int a = 3;
        int b = Math.random();
        System.out.println("b : " + b);
    }
 
    public static void main(String[] args){
        RandomS2 rs2 = new RandomS2();
        rs2.m1();
    }
}

error : incompatioble type : possible lossy conversion from fouble to int

에러 : 호환되지 않는 타입 : double 에서 int 로 변형시에 정보손실 가능성이 있다.

int b = Math.random();

import java.util.*;
 
class RandomS2{
    Random random = new Random();
 
    void m1(){        // 방법 2. With Math 
        int a = 3;
        double b = Math.random();    // 0 < 값 < 1
        int c = (int)(a*b);        // 0 , 1 , 2
        System.out.println("c : " + c);
    }
 
    public static void main(String[] args){
        RandomS2 rs2 = new RandomS2();
        rs2.m1();
    }
}

3. 기본

import java.util.*;
 
class RandomS1{        // Random Study 1
    Random random = new Random();
 
    void showRandom(){
        int i = random.nextInt(7);    // 0 ~ (n-1) >> 0 ~ 6 >> 7개
        System.out.println("i : " + i);
    }
 
    public static void main(String[] args){
        new RandomS1().showRandom();
    }
}

0 ~ 6 까지 random.nextInt(7);

0 , 1 , 2 , 3 , 4 , 5 , 6 

즉 7개 중에 하나

2. 응용

import java.util.*;
 
class RandomS1{        // Random Study 1
    Random random = new Random();
 
    void showRandom(){
        int i = random.nextInt(7);    // 0 ~ (n-1) >> 0 ~ 6 >> 7개
        System.out.println("i : " + i);
        switch(i){
            case 0 : System.out.print("일"); break;
            case 1 : System.out.print("월"); break;
            case 2 : System.out.print("화"); break;
            case 3 : System.out.print("수"); break;
            case 4 : System.out.print("목"); break;
            case 5 : System.out.print("금"); break;
            case 6 : System.out.print("토");
        }
        System.out.println("요일");
    }
 
    public static void main(String[] args){
        new RandomS1().showRandom();
    }
}