如何使单个输入同时满足 2 个扫描仪

Question

So I'm making a calculator app, and I'm stucked in this one, I'm wondering if there's a way to make a single input from the user for two scanners at the same time. Because I'm planning to create a Double ( scanner.nextDouble() ) variable while also checking if it's true or false that it is containing a number ( scanner.hasNextDouble() ).

btw, I'm a beginner so I'm sorry if my question is hard to understand.

---

import java.util.Scanner;

public class Actions {
static Scanner scanner = new Scanner(System.in);
private final double x;
private final double y;
private final int operation;

Actions() {
    this.x = getDoubleX();
    this.y = getDoubleY();
    this.operation = getOperation();
    showAnswer();
}

public static double getDoubleX() {
    double temp = 0;
    String temp1;
    boolean temp2 = true;

    System.out.println("input your first number: ");

    while (temp2) {
         /*
    I tried a solution like this. but it didn't work out.
     */
        temp1 = scanner.nextLine();
        temp = Double.parseDouble(temp1);
        if (Double.isNaN(temp)) {
            System.out.println("try again! ");
        } else {
            temp2 = false;
        }
    }

    return temp;
}

public static double getDoubleY() {
    double temp = 0;
    boolean temp1 = true;
    boolean temp2 = false;       //I'm talking about this
    System.out.println("input your second number: ");
    while (temp1) {
        temp = scanner.nextDouble();
        if (!Double.isNaN(temp)){
            temp1=false;
        } else {
            System.out.println("try again!");
        }
    }
    return temp;
}

public static int getOperation() {
    int temp = 0;
    boolean temp1 = true;

    System.out.println("input your desired operation, \n" +
            "1 = addition, 2 = subtraction, 3 = multiplication, 4 = division");
    while (temp1) {
        temp = scanner.nextInt();
        if (temp >= 1 && temp <= 4) {
            temp1 = false;
        } else {
            System.out.println("try again");
        }
    }
    return temp;
}

public void showAnswer() {
    if (x % 1 == 0 & y % 1 == 0) {
        if (operation == 1) {
            System.out.println("the sum is: " + Math.round(x + y));
        } else if (operation == 2) {
            System.out.println("the difference is: " + Math.round(x - y));
        } else if (operation == 3) {
            System.out.println("the product is: " + Math.round(x * y));
        } else {
            System.out.println("the quotient is: " + Math.round(x / y));
        }
    } else {
        if (operation == 1) {
            System.out.println("the sum is: " + (x + y));
        } else if (operation == 2) {
            System.out.println("the difference is: " + (x - y));
        } else if (operation == 3) {
            System.out.println("the product is: " + (x * y));
        } else {
            System.out.println("the quotient is: " + (x / y));
        }
    }
}

}

Answer 1

Don't use two Scanners. It isn't necessary. Try the following (which you may need to adjust for your specific application).

• this will continue to prompt until a valid double is entered.
• then it will break out of the while loop.

Scanner scan = new Scanner(System.in);
double d = 0;
while (true) {
    System.out.print("Enter a double value: ");
    String possibleDouble = scan.next();
    try {
        d = Double.parseDouble(possibleDouble);
        break;
    } catch (NumberFormatException ne) {
        System.out.printf("bad input (%s) - try again!%n", 
                         possibleDouble);
    }
}
System.out.println(d);

You could put the above in a method with specific args to validate input.