想通了。多谢你们。我知道这不是一个完美的答案，但是我是java新手。
包Dr._Coles_Practice_Problems；
导入java.util.Scanner;
公共(public)类 GpaCalc {
public static void main(String[] args) {
// Needed variables
double credits = 0.0;
double totalcredits = 0.0;
double grade = 0.0;
double qualitypoints = 0;
int classes;
String lettergrade;
Scanner input = new Scanner(System.in);
System.out.println("Enter the amount of classes for this semester");
classes = input.nextInt();
while (classes > 0) {
System.out.println("Enter the amount of credits for this class");
credits = input.nextDouble();
System.out.println("Enter the grade achieved for this class");
lettergrade = input.next();
if (lettergrade.equalsIgnoreCase("a")) {
grade += 4.00;
}
if (lettergrade.equalsIgnoreCase("a-")) {
grade += 3.67;
}
if (lettergrade.equalsIgnoreCase("b+")) {
grade += 3.33;
}
if (lettergrade.equalsIgnoreCase("b")) {
grade += 3.00;
}
if (lettergrade.equalsIgnoreCase("b-")) {
grade += 2.67;
}
if (lettergrade.equalsIgnoreCase("c+")) {
grade += 2.33;
}
if (lettergrade.equalsIgnoreCase("c")) {
grade += 2.00;
}
if (lettergrade.equalsIgnoreCase("c-")) {
grade += 1.67;
}
if (lettergrade.equalsIgnoreCase("d+")) {
grade += 1.33;
}
if (lettergrade.equalsIgnoreCase("d")) {
grade += 1.00;
}
if (lettergrade.equalsIgnoreCase("f")) {
grade += 0.00;
}
classes--;
totalcredits += credits;
}
qualitypoints = grade * credits;
// GPA is calculated via total credits / total quality points
//of which are calculated by multiplying the credit(s) * the quality point value
System.out.println("Your total credit(s)are: " + totalcredits);
System.out.println("Your total quality points are: " + qualitypoints);
System.out.println("Your GPA is: " + (qualitypoints / totalcredits));
}
}
/*
布鲁姆斯堡大学的评分标准
A = 4.00 卓越成就
A- = 3.67
B+ = 3.33
B = 3.00 高于平均水平
B-=2.67
C+ = 2.33
C = 2.00 平均成绩
C- = 1.67
D+=1.33
D = 1.00 最低达到
F = 0.00 失败
*/
最佳答案
if (grade.toLowerCase() == "a") {
由于 "a" 和 grade.toLowerCase() 是对象(String 类型)，因此将它们与 == 进行比较 比较对象的引用，而不是字符串的内容。
使用equals()方法。
if (grade.toLowerCase().equals("a")) {
更多地使用equalsIgnoreCase方法来忽略大小写。
if (grade.equalsIgnoreCase("a")) {
关于Java字符串输入比较，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/20160707/