用双精度返回java中的对象？答案

【问题标题】：Returning an object in java with a double?用双精度返回java中的对象？
【发布时间】：2014-09-15 10:19:09
【问题描述】：

我有一个非常简单的解决方案，但我还没有学会如何去做，也不知道如何解决这个问题。

我有一个接口类：

public interface Analyzable { 
  double getAverage();
  GradedActivity getHighest();
  GradedActivity getLowest();
}

这是我的教授给我的。我将他的代码从两个 GradedActivity 更改为 doubles 并且在此代码中返回它们没有问题。但是我无法将它们作为 GradedActivity 的形式返回

public GradedActivity getHighest() {
    double highest = grades[0].getScore();
    for(int i = )......
    //Code works and returns correct number (tested)
    return highest;

这段代码给了我这个错误 "Double 不能转换为 GradedActivity"

这是我的 GradedActivity 代码

public class GradedActivity { 
private double score;

public GradedActivity() {
}

public void setScore(double s) {
    score = s;
}

public double getScore() {
    return score;
}

public char getGrade() {
    char letterGrade;
    if(score >= 90)
        letterGrade = 'A';
    else if(score >= 80)
        letterGrade = 'B';
    else if(score >= 70)
        letterGrade = 'C';
    else if(score >= 60)
        letterGrade = 'D';
    else
        letterGrade = 'F';

    return letterGrade;
}

}

这是课程成绩代码

enter code here

公共类 CourseGrades 扩展 GradedActivity 实现 Analyzable { 私人 GradedActivity[] 等级 = 新的 GradedActivity[4];

public CourseGrades()
{

}

public void setLab(GradedActivity lab)
{
    grades[0] = lab;
}

public void setPassFailExam(PassFailExam passFailExam)
{
    grades[1] = passFailExam;
}

public void setEssay(GradedActivity essay)
{
    grades[2] = essay;
}

public void setFinalExam(FinalExam finalExam)
{
    grades[3] = finalExam;
}



public String toString() {
    String str;
    str = "Lab Score: " + grades[0].getScore() + 
                        "\t\t\tGrade: " + grades[0].getGrade() +  
                "\nP/F Exam Score: " + grades[1].getScore() +
                        "\t\tGrade: " + grades[1].getGrade() + 
                "\nEssay Score: " + grades[2].getScore() + 
                        "\t\tGrade: " + grades[2].getGrade() + 
                "\nFinal Exam Score: " + grades[3].getScore() + 
                        "\t\tGrade: " + grades[3].getGrade();
    return str;
}

public double getAverage() 
{
    double sum = 0;
    for(int i = 0; i < 4; i++) {
        sum += grades[i].getScore();
    }
    double ave = sum/4;
    return ave;
}

public GradedActivity getHighest() {

    double highest = grades[0].getScore();
    for(int i = 1; i < 4; i++) {
        if(grades[i].getScore() > highest)
            highest = grades[i].getScore();         
    }
    return highest;
}

public GradedActivity getLowest() {
    double lowest = grades[0].getScore();
    for(int i = 1; i < 4; i++) {
        if(grades[i].getScore() < lowest)
            lowest = grades[i].getScore();          
    }
    return setScore(lowest);
}

}

这是界面

公共类 CourseGrades 扩展 GradedActivity 实现 Analyzable { 私人 GradedActivity[] 等级 = 新的 GradedActivity[4];

public CourseGrades()
{

}

public void setLab(GradedActivity lab)
{
    grades[0] = lab;
}

public void setPassFailExam(PassFailExam passFailExam)
{
    grades[1] = passFailExam;
}

public void setEssay(GradedActivity essay)
{
    grades[2] = essay;
}

public void setFinalExam(FinalExam finalExam)
{
    grades[3] = finalExam;
}



public String toString() {
    String str;
    str = "Lab Score: " + grades[0].getScore() + 
                        "\t\t\tGrade: " + grades[0].getGrade() +  
                "\nP/F Exam Score: " + grades[1].getScore() +
                        "\t\tGrade: " + grades[1].getGrade() + 
                "\nEssay Score: " + grades[2].getScore() + 
                        "\t\tGrade: " + grades[2].getGrade() + 
                "\nFinal Exam Score: " + grades[3].getScore() + 
                        "\t\tGrade: " + grades[3].getGrade();
    return str;
}

public double getAverage() 
{
    double sum = 0;
    for(int i = 0; i < 4; i++) {
        sum += grades[i].getScore();
    }
    double ave = sum/4;
    return ave;
}

public GradedActivity getHighest() {

    double highest = grades[0].getScore();
    for(int i = 1; i < 4; i++) {
        if(grades[i].getScore() > highest)
            highest = grades[i].getScore();         
    }
    return highest;
}

public GradedActivity getLowest() {
    double lowest = grades[0].getScore();
    for(int i = 1; i < 4; i++) {
        if(grades[i].getScore() < lowest)
            lowest = grades[i].getScore();          
    }
    return setScore(lowest);
}

}

【问题讨论】：

标签： java inheritance interface subclass superclass

【解决方案1】：

由于双精度不能转换为GradedActivity，您需要先创建一个，设置值（我将创建一个构造函数）然后返回它。

试试

   GradedActivity highGA = new GradedActivity();
   highGA.setScore (highest);
   return highGA;

【讨论】：

【解决方案2】：

您需要获取值并包装在 GradedActivity 实例中并返回它，例如...

public GradedActivity getHighest() {
    double highest = grades[0].getScore();
    for(int i = )......
    //Code works and returns correct number (tested)

    GradedActivity ga = new GradedActivity();
    ga.setScore(highest);
    return ga;

【讨论】：

【解决方案3】：

Java 不会自动从 double 转换为 GradedActivity，您必须创建一个新的 GradedActivity 实例并设置其值。

GradedActivity ga = new GradedActivity(); // create instance
ga.setScore(value); // set value
return ga; // return GradedActivity instead of double

【讨论】：