1.新建项目
file new project 一路默认
创建Main.class

public class Main {
    private static int b = 3;
    public static int fun(int a){
        return a + b;
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int i = scanner.nextInt();
        System.out.println(fun(i));
    }
}