Java FileInputStream 使用 if

Question

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已关闭 10 年前。

我正在做的程序要求我使用 FileInputStream 来计算类(class)的成绩点。

我创建的类 Course 有一个方法:

public double getGradePoint ()
{
    if (letterGrade == "A+" || letterGrade == "A")
        gradePoint = 4.0;
    if (letterGrade == "A-")
        gradePoint = 3.7;
    if (letterGrade == "B+")
        gradePoint = 3.3;
    if (letterGrade == "B")
        gradePoint = 3.0;
    if (letterGrade == "B-")
        gradePoint = 2.7;
    if (letterGrade == "C+")
        gradePoint = 2.3;
    if (letterGrade == "C")
        gradePoint = 2.0;
    if (letterGrade == "C-")
        gradePoint = 1.7;
    if (letterGrade == "D+")
        gradePoint = 1.5;
    if (letterGrade == "D")
        gradePoint = 1.0;
    if (letterGrade == "F")
        gradePoint = 0.0;

    return gradePoint;
}

在测试客户端中我有:

String subject;
String number;
String letGrade;

Course course1 = new Course ("ENGL", "1111", "D+");
FileInputStream file1 = new FileInputStream ("test transcript 1.txt");
Scanner readFile = new Scanner (file1);

while (readFile.hasNext ())
{
    course1.setSubject (readFile.next ());
    subject = course1.getSubject ();
    course1.setNumber (readFile.next ());
    number = course1.getNumber ();
    course1.setLetterGrade (readFile.next ());
    letGrade = course1.getLetterGrade ();
    course1.getGradePoint ();
    System.out.println (course1.toString ());
}

测试成绩单1.txt包含:

COMP 1631   A-
ENGL 1101   B
MATH 1200   C+

但由于某种原因，当我使用 course1.getGradePoint () 时，它总是返回 0.0

运行程序后:

COMP 1631   A-  (worth = 0.0)
ENGL 1101   B   (worth = 0.0)
MATH 1200   C+  (worth = 0.0)

我尝试在 while 命令上方使用 course1.getGradePoint ()，如下所示:

String subject;
String number;
String letGrade;

Course course1 = new Course ("ENGL", "1111", "D+");
course1.getGradePoint ();

FileInputStream file1 = new FileInputStream ("test transcript 1.txt");
Scanner readFile = new Scanner (file1);

while (readFile.hasNext ())
{
    course1.setSubject (readFile.next ());
    subject = course1.getSubject ();
    course1.setNumber (readFile.next ());
    number = course1.getNumber ();
    course1.setLetterGrade (readFile.next ());
    letGrade = course1.getLetterGrade ();
    course1.getGradePoint ();
    System.out.println (course1.toString ());
}

返回为:

COMP 1631   A-  (worth = 1.5)
ENGL 1101   B   (worth = 1.5)
MATH 1200   C+  (worth = 1.5)

出于某种原因，它无法与 readFile.next () 一起使用。如果有人能帮助我，我将不胜感激。

Answer 1

- Java 中的 对象 使用 equals() 和 String 进行比较> 在 Java 中是一个 Object，因此它遵循相同的规则。

- == 将用于比较 原始或检查是否两个或多个 对象引用变量是否指向堆上的同一个对象。

- 因此，您应该使用 equals() 或 equalsIgnoreCase() (如果大小写不重要)来比较 字符串对象。

例如:

if (str1.equals(str2)){}