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Question

我开始Java类，这是我的第一个代码，所以请温柔;）

//importing libraries 
import java.io.*; 
import javax.swing.*; 

public class SongCollection {//class 

//declaring arrays to hold user inputs 
static String title[]={"","",""}; 
static String artist[]={"","",""}; 
static double length[]={0,0,0}; 

static int arrayindex=0;//declaring an index to keep track of arrays 

public static void main(String[] args) throws IOException{//main method 
    menu();//calling menu method 
} 

public static void menu() throws IOException{//menu method 
    String s=JOptionPane.showInputDialog("Choose a menu option\n" +//taking user input and storing it into a string 
      "1: Add Song\n" + 
      "2: Search for a song\n" + 
      "3: Edit a song\n" + 
      "4: Sort songs\n" + 
      "5: Print songs\n" + 
      "6: Save songs to file\n" + 
      "7: Read songs from file\n" + 
      "8: Exit"); 
    int menu=Integer.parseInt(s);//converting user input into a number 

    switch(menu){//going to the appropriate method depending on what number the user presses on the keyboard 
    case 1: add(); break; 
    case 2: search(); break; 
    case 3: edit(); break; 
    case 4: sort(); break; 
    case 5: print(); break; 
    case 6: tofile(); break; 
    case 7: fromfile(); break; 
    case 8: System.exit(0); break; 
    default: JOptionPane.showMessageDialog(null,"Please choose a valid option"); break; 
    } 
} 

public static void add() throws IOException{//add method 
    if(arrayindex>=title.length){//checking if the array is full 
     JOptionPane.showMessageDialog(null,"Song collection is full"); 
     menu(); 
    } 

    //taking the user input and storing them into variables 
    String newtitle=JOptionPane.showInputDialog("Enter the song title:"); 
    String newartist=JOptionPane.showInputDialog("Enter the artist of the song:"); 
    String s=JOptionPane.showInputDialog("Enter the length of the song:"); 
    double newlength=Double.parseDouble(s);//converting length into a number 

    //taking the variables and storing them in the arrays 
    title[arrayindex]=newtitle; 
    artist[arrayindex]=newartist; 
    length[arrayindex]=newlength; 
    arrayindex+=1;//incrementing one to the array index because one new entry was added 

    menu(); 
} 

public static void search() throws IOException{//search method 
    String key=JOptionPane.showInputDialog("Enter your search key: ");//taking in the users search key 

    for(int i=0; i<title.length; i++){ 
     if(key.equals(title[i]) || key.equals(artist[i]) || key.equals(length[i])){//checking if the key is in any of the arrays 
      JOptionPane.showMessageDialog(null,title[i]+", "+artist[i]+", "+length[i]);//printing out the found key 
      menu(); 
     } 
    } 
    JOptionPane.showMessageDialog(null,"Key not found");//if the loop completes the key doesnt exist 
} 

public static void edit() throws IOException{//edit method 
    String s=JOptionPane.showInputDialog("Which entry do you want to edit. Enter a whole number between 0 and " + (arrayindex-1));//asking the user which entry they want to edit 
    int edit=Integer.parseInt(s);//converting user input into a number 

    if(edit>arrayindex || edit<0){//checking if they enter a valid entry that can be editted 
     JOptionPane.showMessageDialog(null,"The entry you entered is does not exist"); 
     menu(); 
    } 

    //taking new entries from the user 
    String newtitle=JOptionPane.showInputDialog("Enter the new song title:"); 
    String newartist=JOptionPane.showInputDialog("Enter the new artist of the song:"); 
    String s2=JOptionPane.showInputDialog("Enter the new length of the song:"); 
    double newlength=Double.parseDouble(s2); 

    //storing them into the array replacing what was previously stored in that index 
    title[edit]=newtitle; 
    artist[edit]=newartist; 
    length[edit]=newlength; 
    menu(); 
} 

public static void sort(){//sort method 
    //nested loop to loop through all elements and make swap when needed 
    for(int i=0; i<title.length-1; i++) 
    { 
     for (int i1=0; i1<title.length-1; i1++) 
     { 
      //storing title current index and title next into 2 different variables 
      String t1 = title[i1]; 
      String t2 = title[i1 + 1]; 

      //storing artist current index and artist next index into 2 different variables 
      String a1 = artist[i1]; 
      String a2 = artist[i1 + 1]; 

      //storing length current index and length next index into 2 different variables 
      double l1 = length[i1]; 
      double l2 = length[i1 + 1]; 

      //comparing title current index with title next index using the compareto method 
      if ((t1).compareTo(t2) > 0) 
      { 
       //creating a temporary variable to store the first variable and then swapping the 2 around 
       String t3 = t1; 
       title[i1] = t2; 
       title[i1 + 1] = t3; 

       String a3 = a1; 
       artist[i1] = a2; 
       artist[i1 + 1] = a3; 

       Double l3 = l1; 
       length[i1] = l2; 
       length[i1 + 1] = l3; 
      } 
     } 
    } 
} 

public static void print() throws IOException{//print method 
    //looping through and printing out each element 
    for(int i=0; i<title.length; i++) 
    { 
     JOptionPane.showMessageDialog(null,title[i]+","+artist[i]+","+length[i]); 
    } 
    menu(); 
} 

public static void tofile() throws IOException{//tofile method 
    final FileWriter fw=new FileWriter("SongCollection.txt");//declaring filewriter 
    final BufferedWriter bw=new BufferedWriter(fw);//delcaring buffer 
    final PrintWriter pw=new PrintWriter(bw);//declaring print writer 

    //looping through array 
    for(int i=0; i<title.length; i++) 
    { 
     pw.println(title[i]+","+artist[i]+","+length[i]);//using print writer to write all 3 elements on one line 
    } 
    pw.close();//closing the writer 
    menu(); 
} 

public static void fromfile() throws IOException{//from file method 
    final FileReader inf=new FileReader("SongCollection.txt");//declaring file reader 
    final BufferedReader ib=new BufferedReader(inf);//declaring buffer reader 
    String s;//string to hold read lines from file 

    while((s=ib.readLine())!=null)//looping through the file while the lines are not empty 
    { 
     JOptionPane.showMessageDialog(null,s);//outputting the read in data to the screen 
    } 
} 
} 

我有几个问题：

我如何添加歌曲界面有一个按钮可以回到主菜单？类似的其他界面？

Answer 1

这是一个经典的初学者错误：你的班级做得太多了。把事情分解一下。

一首歌类，它封装的东西放在一起：

package model; 

public class Song { 
    private String title; 
    private String author; 
    private int length; 
    // You add the rest. 
} 

不要使用基本类型数组;改为使用Java collections。

从模型类中分离出UI的东西。可以在不改写所有代码的情况下更改UI。

Answer 2

你真的应该使用Vector或ArrayList，而不是那些String []数组。否则，你基本上说用户不可能输入三个以上的输入。即使他们可以，或者你将不得不调整你的数组的大小，或者你会有数组outoutofbounds异常。

通过声明一个Vector或ArrayList，你可以继续添加元素（同时你仍然有可用的内存），并且它可以防止出现数组越界的情况，你可能会遇到一个原始字符串数组。