错误：二元运算符 '&&' 第一种类型 int 和第二种类型 boolean 的错误操作数类型

Question

I am new to java and I really enjoy this new learning experience. I got assigned a task where we have to create a simple calendar where the user needs to put a date and the program needs to tell you if it is a correct date.

However, I receive an error code that I'm using a bad operand type. I cant use an int with a boolean type. However, I do not seem to be able to find the problem.

All help and insight is very welcome

public static void main(String[] args) {
    
    Scanner userInput = new Scanner(System.in);  // Creating the new Scanner
    
    System.out.print("Choose a day: ");            //Asking for user to introduce a day
    int day = userInput.nextInt();
    
    System.out.print("Choose a month: ");           // Asking user to introduce a month
    int month  = userInput.nextInt(); 
    
    System.out.print("Choose a year: ");            //Asking user to introduce a year
    int year  = userInput.nextInt(); 
    
    
    if ( (1<= day <= 31) && (1 <= month <= 12) && (year >= 0)){     //marking the limits of day, month and year
        System.out.println(" Congratulations, the date you introduced : " + day + month + year +"exists!!");
    } else if ( (day > 30) && (month = 2 || 4 || 6 || 9 || 10) && (year >= 0)){             //marking the months which have 30 days
        System.out.println(" Oh no, the date you introduced : " + day + month + year +" does Not exists!! You can always try again");
    }else if ( (day > 28) && (month = 2) && (year >=0)){                //marking month February
       System.out.println(" Oh no, the date you introduced : " + day + month + year +" does Not exists!! You can always try again");
    } else {
        System.out.println(" Oh no, the date you introduced : " + day + month + year +" does Not exists!! You can always try again");
    }

}

Answer 1

You must use if ( (day >= 1 && day <= 31) && (month >= 1 && month <= 12) && (year >= 0)) Also, for every month you need to put month == 2 || month == 4... month == 2 || month == 4...