Question

此代码将不会在多个ORS（即||）上执行if语句，而且我不知道为什么，有人可以提供帮助吗？ Java的新手。

    if (!"A123".equals(itemNumber) || !"A55".equals(itemNumber) || !"B750".equals(itemNumber) 
                                   || !"C650".equals(itemNumber))
    {
        System.out.print("\nInvalid Item. Try again. ");
        System.out.print("\nEnter an item number or END to exit: ");
        itemNumber = keyboard.nextLine();
    }
    System.out.printf("\nThank you. %s", itemNumber);

Answer 1

在您的代码中，您要问“如果项目编号不等于“ A123”或“ A55”或“ B750”或“ C650”，请执行这些操作”。因此，当您输入“ A55”时，程序会检查“ A55”不等于“ A123”或“ A55”。...哦，它不等于“ A123”，因此条件为真。

如果您更改这样的要求。 “如果项目编号不等于“ A123”，“ A55”，“ B750”和“ C650”，请执行这些操作”。因此，当您输入“ A55”时，程序会检查“ A55”不等于“ A123”和“ A55” ...哦，它不等于“ A55”，因此条件为假。例子

if (!"A123".equals(itemNumber) && !"A55".equals(itemNumber) && !"B750".equals(itemNumber) && !"C650".equals(itemNumber))
{
    System.out.print("\nInvalid Item. Try again. ");
    System.out.print("\nEnter an item number or END to exit: ");
    itemNumber = keyboard.nextLine();
}
System.out.printf("\nThank you. %s", itemNumber);

或者您可以将您的要求更改为类似的内容， “如果项目编号等于“ A123”或“ A55”或“ B750”或“ C650”，则打印“谢谢”，否则请执行这些操作。”这是正确的。例子

if ("A123".equals(itemNumber) || "A55".equals(itemNumber) || "B750".equals(itemNumber) || "C650".equals(itemNumber))
{
    System.out.printf("\nThank you. %s", itemNumber);
}
else{
    System.out.print("\nInvalid Item. Try again. ");
    System.out.print("\nEnter an item number or END to exit: ");
    itemNumber = keyboard.nextLine();
}

Answer 2

您可能想使用“ AND”运算符代替“ OR”：

public MainPage()
{
    this.InitializeComponent();
    ObservableCollection<StudentsList> studentsLists = new ObservableCollection<StudentsList>();
    studentsLists.Add(new StudentsList() { StudentName = "first student" });
    studentsLists.Add(new StudentsList() { StudentName = "second student" });
    studentsLists.Add(new StudentsList() { StudentName = "third student" });
    studentsLists.Add(new StudentsList() { StudentName = "fourth student" });
    studentsLists.Add(new StudentsList() { StudentName = "fifth student" });

    _ClassRoomDetailsList.StudentsArray = studentsLists;

    //assigned values to observable collection here
    list1.ItemsSource = _ClassRoomDetailsList.StudentsArray;
}
public ClassRoomDetailsList _ClassRoomDetailsList = new ClassRoomDetailsList();

表示“如果if (!"A123".equals(itemNumber) && !"A55".equals(itemNumber) && !"B750".equals(itemNumber) && !"C650".equals(itemNumber)) { System.out.print("\nInvalid Item. Try again. "); System.out.print("\nEnter an item number or END to exit: "); itemNumber = keyboard.nextLine(); } System.out.printf("\nThank you. %s", itemNumber);不等于A123并且itemNumber不等于A55并且itemNumber不等于B750并且itemNumber不等于C650“

更好的方法是使用itemNumber语句：

switch

Answer 3

您的错误是您使用'或'操作。您应该对此操作使用'AND'操作。同样，如果对此问题使用Arrays.asList和contains（）方法，我认为这很简单。

if (!"A123".equals(itemNumber) && !"A55".equals(itemNumber) && !"B750".equals(itemNumber)  && !"C650".equals(itemNumber))
{

    System.out.print("\nInvalid Item. Try again. ");
    System.out.print("\nEnter an item number or END to exit: ");
    itemNumber = keyboard.nextLine();
}

    System.out.printf("\nThank you. %s", itemNumber);

Java不等于字符串语法不起作用

3 个答案: