下一步扫描之前，如何检查扫描仪是否有输入

Question

在分离标记之前，我试图检查扫描仪是否有多个标记。我目前正在尝试使用扫描仪。hasNext（）（我的扫描仪的名字是sc）。如果用户输入“string int”，那么我不想打印“enter age”或“enter grade”

System.out.println("Enter name or command: ");
            name = sc.next();
            if(name.toLowerCase().equals("next")) {
                students.remove(0);
            }else if(name.toLowerCase().equals("end")) {
                running = false;
            }else {
//This is where it gets dicey
                if(!sc.hasNext())
                    System.out.println("Enter age: ");
                age = sc.nextInt();
                if(!sc.hasNext())
                    System.out.println("Enter grade: ");
                grade = sc.nextInt();

                if(first) {
                    students.add(new Student(name, age, grade));
                    first = false;
                }else {
                    addStudent(new Student(name, age, grade), students.get(students.size()-1));
                }
            }

目前，无论输入是什么，我的程序都会跳过if语句。如果我把它拿走！然后，即使输入是一行，这些行也会打印出来。他们似乎也打印后，下一个是我发现奇怪的。我将非常感谢您的帮助！

Answer 1

我不得不做一些修改，因为它不会编译。当我运行它时，它给了我你说你想要的：

C:\Users\..snip..\stackOverflow>java src\stackOverflowTest.java
Enter name or command:
Peter 78 34
addStudent(new Student(name, age, grade), students.get(students.size()-1));

然而，如果我只输入一个参数，它就会挂起（根据javaDoc：“这个方法可能会在等待输入扫描时阻塞。”）：

C:\Users\..snip..\stackOverflow>java src\stackOverflowTest.java
Enter name or command:
hello

这是可编译的修改：

import java.util.Scanner;

public class StackOverflowTest {
  static String name;
  static int age;
  static int grade;
  static boolean first;
  static boolean running;

  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println("Enter name or command: ");
      name = sc.next();
      if(name.toLowerCase().equals("next")) {
            System.out.println("students.remove(0);");
//          students.remove(0);
      }else if(name.toLowerCase().equals("end")) {
          running = false;
      }else {

//This is where it gets dicey
        if(!sc.hasNext())
            System.out.println("Enter age: ");
        age = sc.nextInt();
        if(!sc.hasNext())
            System.out.println("Enter grade: ");
        grade = sc.nextInt();

        if(first) {
            System.out.println("students.add(new Student(name, age, grade));");
//            students.add(new Student(name, age, grade));
            first = false;
        }else {
            System.out.println("addStudent(new Student(name, age, grade), students.get(students.size()-1));");
//            addStudent(new Student(name, age, grade), students.get(students.size()-1));
        }
      }
  }
}

如果你想让所有选项都保持打开状态，你可以这样做（注意这里没有异常处理）：

import java.util.Scanner;

public class StackOverflowTest {
  static String name = "";
  static int age = -1;
  static int grade = -1;

  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println("Enter name or command: ");


    String[] input = sc.nextLine().split(" ");
    switch (input.length) {
      case 3: grade = Integer.valueOf(input[2]);
              // fallthrough
      case 2: age = Integer.valueOf(input[1]);
              // fallthrough
      case 1: name = input[0];
    };

    if (name.isEmpty()) {
      System.out.println("Enter name: ");
      name = sc.next();
    }   

    if (age == -1) {
      System.out.println("Enter age: ");
      age = sc.nextInt();
    }   

    if (grade == -1) {
      System.out.println("Enter grade: ");
      grade = sc.nextInt();
    }
  }
}