有没有人介意帮我排查代码故障，我正在尝试导入我创建的一个类，结果得到“cannot resolve error”

Question

java新手，需要一些帮助。我正在处理2个文件。一个类定义一个类及其所有方法，另一个类构造该类的一个实例。我的项目要求我们将类方法的输出写入到file.When中，我尝试将文件1导入到文件2中，但一直收到“无法解析”错误。

文件#1

public class ViolinGonzalezAP3 {
    //Create Violin class
        public int numberOfStrings = 4;
        public char[] stringNames = {'E', 'A', 'D', 'G'};
        public boolean isTuned = false;
        public boolean isPlaying = false;
        public int numberOfViolins = 0;
    class Violin{
        //Create methods for Violin class
        public Violin(){
            numberOfViolins++;
        }
        public void startPlaying() {
            isPlaying = true;
            System.out.println(" violin is now playing.");
        }
        public void stopPlaying() {
            isPlaying = false;
            System.out.println(" violin has stopped playing.");
        }
        public void tuneOn() {
            isTuned = true;
            System.out.println(" violin is now tuned.");
        }
        public void tuneOff() {
            isTuned = false;
            System.out.println(" violin is untuned.");
        } 
        int getNumberOfViolins(){
            return numberOfViolins;
        }
        int getNumberOfStrings(){
            return numberOfStrings;
        }
        char[] notes(){
            return stringNames;
        }
    }
}       

文件#2

import java.io.*;
import java.util.Arrays;

public class ViolinDriverGonzalezAP3 {
    public static void main(String[] args) throws Exception{
        //Declare file and class names
        java.io.File file = new java.io.File("Java violinOutput.txt");
        PrintWriter output = new PrintWriter(file);
        Violin[] violinAmount = new Violin[10];
        //Create 10 violin objects
        for (int i = 0; i < violinAmount.length; i++){
            violinAmount[i] = new Violin();
            System.out.println(Violin.getNumberOfViolins() + " Violin");
            output.println(Violin.getNumberOfViolins() + " object:");
            violinAmount[i].tuneOff();
            output.println("The violin is now tunning...");
            violinAmount[i].tuneOn();           
            output.println("The violin is now playing...");
            violinAmount[i].startPlaying();
            output.println("String numbers is " + Violin.getNumberOfStrings() + " with String names are " + Arrays.toString(Violin.notes()));
            output.println("The violin is now stopped");
            violinAmount[i].stopPlaying();
        }
        output.close();
   }
}

Answer 1

为了创建内部类的实例，您必须首先创建一个外部类的实例。检查此代码。

import java.io.*;
import java.util.Arrays;
public class ViolinDriverGonzalezAP3 {

    public static void main(String[] args) throws Exception{
        //Declare file and class names
        java.io.File file = new java.io.File("Java violinOutput.txt");
        PrintWriter output = new PrintWriter(file);
        ViolinGonzalezAP3 outerClassObj = new ViolinGonzalezAP3();

        ViolinGonzalezAP3.Violin[] violinAmount = new ViolinGonzalezAP3.Violin[10];
        //Create 10 violin objects
        for (int i = 0; i < violinAmount.length; i++){
            violinAmount[i] = outerClassObj.new Violin();
            System.out.println(violinAmount[i].getNumberOfViolins() + " Violin");
            output.println(violinAmount[i].getNumberOfViolins() + " object:");
            violinAmount[i].tuneOff();
            output.println("The violin is now tunning...");
            violinAmount[i].tuneOn();           
            output.println("The violin is now playing...");
            violinAmount[i].startPlaying();
            output.println("String numbers is " + violinAmount[i].getNumberOfStrings() + " with String names are " + Arrays.toString(violinAmount[i].notes()));
            output.println("The violin is now stopped");
            violinAmount[i].stopPlaying();
        }
        output.close();
   }

}

Answer 2

尝试修改第二个类：

import java.io.*;
import java.util.Arrays;

public class ViolinDriverGonzalezAP3 {
public static void main(String[] args) throws Exception{
    //Declare file and class names
    java.io.File file = new java.io.File("Java violinOutput.txt");
    PrintWriter output = new PrintWriter(file);
    ViolinGonzalezAP3 vg = new ViolinGonzalezAP3();
    ViolinGonzalezAP3.Violin[] violinAmount = new ViolinGonzalezAP3.Violin[10];
    //Create 10 violin objects
    for (int i = 0; i < violinAmount.length; i++){
        violinAmount[i] = vg.new Violin();
        System.out.println(violinAmount[i].getNumberOfViolins() + " Violin");
        output.println(violinAmount[i].getNumberOfViolins() + " object:");
        violinAmount[i].tuneOff();
        output.println("The violin is now tunning...");
        violinAmount[i].tuneOn();           
        output.println("The violin is now playing...");
        violinAmount[i].startPlaying();
        output.println("String numbers is " + violinAmount[i].getNumberOfStrings() + " with String names are " + Arrays.toString(violinAmount[i].notes()));
        output.println("The violin is now stopped");
        violinAmount[i].stopPlaying();
    }
    output.close();
   }
}//end method main

Answer 3

代码为Violin类返回cannot resolve错误的原因是因为该类在ViolinGonzalezAP3中被定义为内部类。

虽然仍然可以在代码的其他部分实例化和引用内部类，但这样做应该有很好的理由。在您的特定情况下，我建议避免这样做，只需按如下方式公开小提琴类：

文件: Violin.java

class Violin{

    private static int numberOfViolins = 0;
    private static final int numberOfStrings = 4;
    private static final char[] stringNames = {'E', 'A', 'D', 'G'};
    private boolean isTuned = false;
    private boolean isPlaying = false;

    //Create methods for Violin class
    public Violin(){
        numberOfViolins++;
    }
    public void startPlaying() {
        isPlaying = true;
        System.out.println(" violin is now playing.");
    }
    public void stopPlaying() {
        isPlaying = false;
        System.out.println(" violin has stopped playing.");
    }
    public void tuneOn() {
        isTuned = true;
        System.out.println(" violin is now tuned.");
    }
    public void tuneOff() {
        isTuned = false;
        System.out.println(" violin is untuned.");
    } 
    public static int getNumberOfViolins(){
        return numberOfViolins;
    }
    public static int getNumberOfStrings(){
        return numberOfStrings;
    }
    public static char[] notes(){
        return stringNames;
    }
}

请详细查看这个类，因为您将在此处找到对原始代码的更多更改：

methods

• numberOfStrings和modified

• numberOfViolins参数被定义为静态，因为它们是常量，不会是静态的，从而保持创建的小提琴的全局数量(注意:有更好的方法来解决这个任务，即可以将保持实例数量的责任移到ViolinDriverGonzalezAP3上，但现在就可以了)。和private已经定义为静态的，以保持创建的小提琴的全局数量。
• 方法getNumberOfViolins、getNumberOfStrings和notes已定义为public static，因此可以通过Violin.<methodName>

将它们作为类方法进行访问