Question

我一直收到这个错误：

线程中的异常＆＃34; main＆＃34;显示java.lang.NullPointerException

at ButtonsLab.pvc1（ButtonsLab.java:110）

at ButtonsLab.main（ButtonsLab.java:155）

有些人问过这个问题，但我似乎无法找到解决这个问题的人。我知道它与pvc1（）方法中的数组有关。

import java.util.Scanner;
import java.util.ArrayList;
import java.util.Random;

class ButtonsLab
{
   ArrayList<Integer> buttons;

ButtonsLab(){
   buttons = new ArrayList<Integer>();
}

  public void fillMyArray(){
     for(int i = 0; i < 5; i++){
     buttons.add(i + 1);
  }
}

public static int pvp(int buttonNum){

  Scanner in = new Scanner(System.in);
  int player1 = 0;
  int player2 = 0;
  int x = 0; //determines who wins

  while (buttonNum > 1){

     while (player1 < 1 || player1 > 3){

        System.out.println("Player 1: How many buttons do you take?(1-3)");

        player1 = in.nextInt();

     }

     buttonNum -= player1;

     if(buttonNum != 1){
        System.out.println("There are " + buttonNum + " Buttons on the board.");
     }
     else{
        System.out.println("... There is 1 Button on the board.");
     }

     if(buttonNum == 1){

        x = 1;

     }

     else{
        while (player2 < 1 || player2 > 3){

           System.out.println("Player 2: How many buttons do you take?(1-3)");

           player2 = in.nextInt();

        }
     }

     buttonNum -= player2;

     if(buttonNum != 1){
        System.out.println("There are " + buttonNum + " Buttons on the board.");
     }
     else if(x !=1){
        System.out.println("... There is 1 Button on the board.");
     }

     player1 = 0;
     player2 = 0;

  }

  if(x == 1){
     while (player2 < 1 || player2 > 3){

        System.out.println("Player 2: How many buttons do you take?(1-3)");

        player2 = in.nextInt();

     }

     System.out.println("Player 2, you lose.");
  }
  else{
     while (player1 < 1 || player1 > 3){

        System.out.println("Player 1: How many buttons do you take?(1-3)");

        player2 = in.nextInt();

     }

     System.out.println("Player 1, you lose.");

  }
  return x;
}

public static int pvc1(int buttonNum){
  Scanner in = new Scanner(System.in);
  int player1 = 0;
  int x = 0; //determines who wins

  ButtonsLab [] aiChoice;
  aiChoice = new ButtonsLab[buttonNum];

  for(int i = 0; i < aiChoice.length; i++){
     aiChoice[i].fillMyArray();
  }

  while (buttonNum > 1){
     while (player1 < 1 || player1 > 3){

        System.out.println("Player 1: How many buttons do you take?(1-3)");

        player1 = in.nextInt();

     }

     buttonNum -= player1;

     int rnd = new Random().nextInt(aiChoice.length);
     System.out.println("AI selects " + rnd);

     player1 = 0;

  }
  return x;
}

public static void main (String[] args)
{
  Scanner in = new Scanner(System.in);
  int buttonNum = 0;
  int gameOpt = 0;

  while (buttonNum < 10 || buttonNum > 100){

     System.out.println("How many buttons are on the board initially?(10-100)");

     buttonNum = in.nextInt();
  }

  System.out.println("Options: Play against a friend (1) Play against easy computer (2) Play against hard computer (3)");

  gameOpt = in.nextInt();

  switch(gameOpt){
     case 1:
        pvp(buttonNum);
        break;
     case 2:
        pvc1(buttonNum);
        break;


  }

}

}

Answer 1

完成此操作后

aiChoice = new ButtonsLab[buttonNum];

数组中充满了＆＃39; nulls＆＃39;。你需要这样做（对于数组中的每个位置）

aiChoice[i] = new ButtonsLab();

之前你可以这样做：

aiChoice[i].fillMyArray();

无法修复错误线程中的异常＆＃34; main＆＃34;显示java.lang.NullPointerException

1 个答案: