如何调用非静态方法（数组）

Question

我正在尝试调用我的 add 方法来向我的数组添加分数 到目前为止我已经得到了这个，但我一直收到一个错误，说 myQuiz 从未初始化过。 ..................................................... .....................................

import java.util.Scanner;
public class Assignment7 {
public static void main (String[] args) {
       //new scanner
       Scanner in = new Scanner (System.in);
       String choice;
       char command;
       // print the menu
       int count = 0;
       int counter = 0;
       printMenu();
       int array[] = new int[0];
      //do while loop testing using user input 
       do{
           // ask a user to choose a command
           System.out.println("\nPlease enter a command or type ?");
           choice = in.next().toLowerCase();
           command = choice.charAt(0);
           //start switch statement for user input cases
           switch (command)
            {
                 switch (command)
            {
                 case 'n':  //ask and read the size of the input array and name
                     System.out.print("\n\t n [Create a new Quiz]: ");
                     System.out.print("\n\t  [Input the size of quizzes]: ");
                     int num=in.nextInt(); // read the integer
                     array = new int[num];
                     System.out.print("\n\t  [Input the name of the student]: ");
                     String name = in.next(); //read name
                     Quiz myQuiz = new Quiz(num, name);
                      break;
                 case 'a': //  ask and add score to array
                      System.out.print("\n\t a [Add a score]: ");
                          array[count] = in.nextInt();
                          myQuiz.add(array[count]);
                          counter++;
                      break;
                     /*
                 case 'a': //  ask and add score to array
                      System.out.print("\n\t a [Add a score]: ");
                          array[count] = in.nextInt();
                          myQuiz.add(array[count]); //HELP
                          counter++;
                      break;

还有我的带有添加方法的 Quiz.java

public class Quiz {

private int count;
private int[] scores;
private String name;    
public Quiz(int a,String name){
 scores = new int [a];
 for (int i = 0; i<scores.length; i++){
     scores[i] = -1;
 }
 this.count = 0;
 this.name = "";
 }
public void add(int b){
 for(int i : scores){
 if(scores[i] == count){
    System.out.println("Array is full. The value " + b + " cannot be added.");
 }
 else {
     scores[count] = b;
     count++;
 }

Answer 1

更仔细地观察你的作用域：你在你的 switch-case 语句的一个分支中定义了myQuiz，但你也在另一个分支中访问它。如果访问case 'a' 会发生什么？ myQuiz 变量在那里是未知的！

             case 'n':  //ask and read the size of the input array and name
                 System.out.print("\n\t n [Create a new Quiz]: ");
                 System.out.print("\n\t  [Input the size of quizzes]: ");
                 int num=in.nextInt(); // read the integer
                 array = new int[num];
                 System.out.print("\n\t  [Input the name of the student]: ");
                 String name = in.next(); //read name
                 Quiz myQuiz = new Quiz(num, name);
                  break;
             case 'a': //  ask and add score to array
                  System.out.print("\n\t a [Add a score]: ");
                      array[count] = in.nextInt();
                      myQuiz.add(array[count]);
                      counter++;
                  break;

你必须在你的 switch-case 语句之外定义myQuiz，在它之前，更具体。

Answer 2

你创建一个空数组：

int array[] = new int[0];

并尝试为其分配数字：

array[count] = in.nextInt();

它不能工作。

你必须给它一个正的长度。