java模拟计算器类，没有思路，主要是这输入方式太奇怪了，为什么能在一行输入多个字符和数字啊，求解决代码

目前我的代码：
import java.util.Scanner;
public class 计算类 {
public static double a;
public static double b;
public static String operator;
public static double sum=0;
public static void main(String[] args) {
int number;
Scanner scanner = new Scanner(System.in);
number=scanner.nextInt();
a = scanner.nextDouble();
operator = scanner.next();
b = scanner.nextDouble();
switch (operator) {
case "+":
sum = add(a, b);
System.out.println(sum);
break;
case "-":
sum = subtract(a, b);
System.out.println(sum);
break;
case "":
sum = multiply(a, b);
System.out.println(sum);
break;
case "/":
sum = divide(a, b);
System.out.println(sum);
break;
}
}
public static double add(double a,double b){
return a+b;
}
//减
public static double subtract(double a,double b){
return a-b;
}
//乘
public static double multiply(double a,double b){
return ab;
}
//除
public static double divide(double a,double b){
return a/b;
}
}
只能做到单行输入字符和数字，单行输出结果

你多行输入是一样的，只要不用nextLine()接收。

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