if语句if-else仅在java中执行else

Question

所以我正在努力解决这个问题，似乎我无法理解，我对java一无所知，我需要帮助。。因此，我正在制作一个简单的程序，它将通过分数来确定你是否通过了该科目，而它似乎只决定了ELSE语句。。这是密码。。这对我真的很有帮助。。提前谢谢

    String studID=" ",course=" ", name=" ", dept=" ", subj=" ";
    double exam1=0, exam2=0, exam3=0, exam4=0;
    double avg, pgrade;
    String msg=" ";

studID =JOptionPane.showInputDialog("Please fill-out the following fields:"
        + "\nStudent ID: ");
name = JOptionPane.showInputDialog("Name: ");
dept = JOptionPane.showInputDialog("Department: ");
course = JOptionPane.showInputDialog("Course: ");
subj = JOptionPane.showInputDialog("Subject: ");
exam1 = Double.parseDouble(JOptionPane.showInputDialog("First Examination: "));
exam2 = Double.parseDouble(JOptionPane.showInputDialog("Second Examination: "));
exam3 = Double.parseDouble(JOptionPane.showInputDialog("Third Examination: "));
exam4 = Double.parseDouble(JOptionPane.showInputDialog("Final Examination: "));
avg = (exam1 + exam2 + exam3 + exam4)/4;
pgrade =(100 - avg + 10) / 10;

if (avg==100)
{
    msg = "passed - Excellent!";
}else if (avg>100 && avg<89)
{
    msg = "Passed - Very Good!";
}else if (avg>90 && avg<84)
{
    msg = "Passed - Average";
}else if (avg>85 && avg<79)
{
    msg = "Passed - Good";
}else if (avg>80 && avg<74)
{
    msg = "Passed - Satisfactory";
}else if (avg>75 && avg<49)
{
    msg = "Failed";
}else if (avg>50 && avg<0.00)
{   
    msg = "Dropped";
}else if (avg==0.00 && avg<0.00)
{
    msg = "No such Grade";
}else
{
    msg = "Out of Range or Invalid.";
}


JOptionPane.showMessageDialog(null, new JTextArea (
        "|======Student Details=======|"
    + "\n|StudentID:\t" + studID +"\t |"
    + "\n|Name:\t" + name + "\t |"
    + "\n|Department:\t" +dept+ "\t |"
    + "\n|Course:\t"+course+"\t |"
    + "\n|Subject:\t"+subj + "\t |"
    + "\n|=======Grade Details======= |"
    + "\n|First     Second     Third     Fourth  |"
    + "\n|"+exam1+"     "+exam2+"     "+exam3+"     "+exam4+"\t     |"
    + "\n|Average:\t" +avg + "\t|"
    + "\n|Point Grade\t:" +pgrade+"\t|"
    + "\n|Remarks:"+msg+"\t|"
    + "\n|=============================|"));





}

}

Answer 1

这个条件是错误的，因为要在一个范围内包含一个变量，您必须进行设置

else if(avg>89 && avg<100)

Answer 2

你的比较一开始就错了，所以试着按照我纠正的方法做一些事情，这不是最好的，这样你就可以改进它

  String studID=" ",course=" ", name=" ", dept=" ", subj=" ";
    double exam1=0, exam2=0, exam3=0, exam4=0;
    double avg, pgrade;
    String msg=" ";

studID =JOptionPane.showInputDialog("Please fill-out the following fields:"
        + "\nStudent ID: ");
name = JOptionPane.showInputDialog("Name: ");
dept = JOptionPane.showInputDialog("Department: ");
course = JOptionPane.showInputDialog("Course: ");
subj = JOptionPane.showInputDialog("Subject: ");
exam1 = Double.parseDouble(JOptionPane.showInputDialog("First Examination: "));
exam2 = Double.parseDouble(JOptionPane.showInputDialog("Second Examination: "));
exam3 = Double.parseDouble(JOptionPane.showInputDialog("Third Examination: "));
exam4 = Double.parseDouble(JOptionPane.showInputDialog("Final Examination: "));
avg = (exam1 + exam2 + exam3 + exam4)/4;
pgrade =(100 - avg + 10) / 10;

if (avg==100)
{
    msg = "passed - Excellent!";
}else if (avg<100 && avg>89)
{
    msg = "Passed - Very Good!";
}else if (avg<90 && avg>84)
{
    msg = "Passed - Average";
}else if (avg<85 && avg>79)
{
    msg = "Passed - Good";
}else if (avg<80 && avg>74)
{
    msg = "Passed - Satisfactory";
}else if (avg<75 && avg>49)
{
    msg = "Failed";
}else if (avg<50 && avg>0.00)
{   
    msg = "Dropped";
}else if (avg==0.00)//no one gets below zero in  a fair system
{
    msg = "No such Grade";
}else
{
    msg = "Out of Range or Invalid.";
}


JOptionPane.showMessageDialog(null, new JTextArea (
        "|======Student Details=======|"
    + "\n|StudentID:\t" + studID +"\t |"
    + "\n|Name:\t" + name + "\t |"
    + "\n|Department:\t" +dept+ "\t |"
    + "\n|Course:\t"+course+"\t |"
    + "\n|Subject:\t"+subj + "\t |"
    + "\n|=======Grade Details======= |"
    + "\n|First     Second     Third     Fourth  |"
    + "\n|"+exam1+"     "+exam2+"     "+exam3+"     "+exam4+"\t     |"
    + "\n|Average:\t" +avg + "\t|"
    + "\n|Point Grade\t:" +pgrade+"\t|"
    + "\n|Remarks:"+msg+"\t|"
    + "\n|=============================|"));





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