Question

我在构造函数中传递一个字符串，并将其值赋给Grade类型的对象类变量。我知道这很简单，但我无法弄清楚这项工作。我无法修改变量或构造函数参数，只能实现构造函数。

我查看了字符串中的方法，但一小时后无法弄清楚要做什么。铸造/转换/ idk

public class Course
{

private String courseNumber;
private int numberOfCredits;
private Grade gradeReceived;
private String termWhenTaken;

/**
 * The value for the courseNumber instance variable is converted to uppercase.
 * The numberOfCredits instance variable is set to the credits passed as a parameter if     it's 0 or more. 
 * Otherwise, it gets set to 0.
 */   
public Course(String course, int credits, String grade, String term) 
{    courseNumber = course.toUpperCase();
     numberOfCredits = credits; 
     termWhenTaken = term;
     gradeReceived = grade;   <-----problem here  mismatched data types obviously
}

Answer 1

您不能将类型A的对象分配给类型B的引用变量（除非A是B的子类）。您无法将String分配给Grade。

您需要使用Grade：

创建String

gradeReceived = new Grade(grade);

new运算符调用构造函数public Grade(String grade)并返回一个新的Grade对象。

Answer 2

您需要某种转换器或映射来将String值（例如，“6th”）转换为Grade对象。这样的事情可以让你开始：

public Course(String course, int credits, String grade, String term) {
    ...
    gradeReceived = convertGradeStringToGrade(grade);
    ...
}

private Grade convertGradeStringToGrade(String gradeStr) {
    if ("A".equals(gradeStr)) {
        return new Grade("A");
    } else if ("B".equals(gradeStr)) {
        return new Grade("B");
    } else if ... etc
    } else {
        // do something (throw an exception? return null?) if the string doesn't match a known grade
    }
}

或者你可以做一些像

这样的事情

public Course(String course, int credits, String grade, String term) {
    ...
    gradeReceived = new Grade(grade);
    ...
}

如果没有任何转换要做。

您也可以为成绩对象使用枚举，但这可能超出了您当前尝试做的范围。

构造函数和不同的数据类型令人困惑

2 个答案: