Question

我必须创建一个Java项目，该项目将在文本文件中作为岛读取并随机移动鼠标100次并确定鼠标是否逃逸，饥饿或淹死。我有2节课。我的第一堂课是：

 import java.util.ArrayList;
 import java.util.List;
 import java.util.Scanner;
 import java.io.File;
 import java.io.FileNotFoundException;

   public class Island {


public char island [][];
private int  MoveCount = 0, StarveCount = 0, DrownCount = 0, EscapeCount = 0;
public  int mouse = 1;

    public void mouseIsland(String fileName) throws FileNotFoundException {
        island = new char [0][0];
        Scanner file = new Scanner(new File(fileName));
        List<String> lines = new ArrayList<String>();
        while(file.hasNextLine()) {  
        ArrayList<String> lines1= new ArrayList<String>();
        String line= file.nextLine();
        lines1.add(line);    
        island=new char[lines1.size()][];
                }

            }


    public void moveLeft() {
       char[][] temp = island;
        if(MoveCount == 100){
            System.out.println("The mouse starved");
            StarveCount++;
            MoveCount = 0;
        }
        for(int i=0; i<island.length; ++i)
            for(int j=0; j<island[i].length; ++j)
                if(MoveCount <100 && island[i][j] == '-'){
                    temp[i][j] = island[i][j-1]; 
                    MoveCount++;
                        if(temp[i][j] == '#'){
                            System.out.println("The mouse drowned after moving "+MoveCount+" times.");
                            DrownCount++;
                            MoveCount = 0;
                            break;
                        }
                        else if(temp[0][j] == '-' || temp [island.length-1][j] == '-' || temp [i][0] == '-' || temp[i][island[0].length-1] == '-'){
                            System.out.println("The mouse found a bridge and escaped after "+MoveCount+" times.");
                            EscapeCount++;
                            MoveCount = 0;
                            break;
                        }

        mouse = temp[i][j];
        temp[i][j] = (char) (MoveCount+1);
        island = temp;    
                }   
    }

        public void moveRight() {
           char[][] temp = island;
            if(MoveCount == 100){
                System.out.println("The mouse starved");
                StarveCount++;
                MoveCount = 0;
            }
            for(int i=0; i<island.length; ++i)
                for(int j=0; j<island[i].length; ++j)
                    if(MoveCount <100 && island[i][j] == '-'){
                        temp[i][j] = island[i][j+1]; 
                        MoveCount++;
                            if(temp[i][j] == '#'){
                                System.out.println("The mouse drowned after moving "+MoveCount+" times.");
                                DrownCount++;
                                MoveCount = 0;
                                break;
                            }
                            else if(temp[0][j] == '-' || temp [island.length-1][j] == '-' || temp [i][0] == '-' || temp[i][island[0].length-1] == '-'){
                                System.out.println("The mouse found a bridge and escaped after "+MoveCount+" times.");
                                EscapeCount++;
                                MoveCount = 0;
                                break;
                            }
            mouse = temp[i][j];
            temp[i][j] = (char) (MoveCount+1);
            island = temp;    
                    } 
        }

    public void moveUp() {
        char[][] temp = island;
        if(MoveCount == 100){
            System.out.println("The mouse starved");
            StarveCount++;
            MoveCount = 0;
        }
        for(int i=0; i<island.length; ++i)
            for(int j=0; j<island[i].length; ++j)
                if(MoveCount <100 && island[i][j] == '-'){
                    temp[i][j] = island[i-1][j]; 
                    MoveCount++;
                        if(temp[i][j] == '#'){
                            System.out.println("The mouse drowned after moving "+MoveCount+" times.");
                            DrownCount++;
                            MoveCount = 0;
                            break;
                        }
                        else if(temp[0][j] == '-' || temp [island.length-1][j] == '-' || temp [i][0] == '-' || temp[i][island[0].length-1] == '-'){
                            System.out.println("The mouse found a bridge and escaped after "+MoveCount+" times.");
                            EscapeCount++;
                            MoveCount = 0;
                            break;
                        }
        mouse = temp[i][j];
        temp[i][j] = (char) (MoveCount+1);
        island = temp;    
                } 
    }

    public void moveDown(){
    char[][] temp = island;
        if(MoveCount == 100){
            System.out.println("The mouse starved");
            StarveCount++;
            MoveCount = 0;
        }
        for(int i=0; i<island.length; ++i)
            for(int j=0; j<island[i].length; ++j)
                if(MoveCount <100 && island[i][j] == '-'){
                    temp[i][j] = island[i+1][j]; 
                    MoveCount++;
                        if(temp[i][j] == '#'){
                            System.out.println("The mouse drowned after moving "+MoveCount+" times.");
                            DrownCount++;
                            MoveCount = 0;
                            break;
                        }
                        else if(temp[0][j] == '-' || temp [island.length-1][j] == '-' || temp [i][0] == '-' || temp[i][island[0].length-1] == '-'){
                            System.out.println("The mouse found a bridge and escaped after "+MoveCount+" times.");
                            EscapeCount++;
                            MoveCount = 0;
                            break;
                        }
        mouse = temp[i][j];
        temp[i][j] = (char) (MoveCount+1);
        island = temp;    
                } 
}

    public  void moveMouse (){   
        for(int i=0; i<100; i++)
        {
            int randomNumber = 1+(int)(Math.random()*(4));
                if(randomNumber == 1);
                    moveUp();
                if(randomNumber == 2);
                    moveDown();
                if(randomNumber == 3);
                    moveLeft();
                if(randomNumber == 4);
                    moveRight();
        }   
    }

    public String printStats(){
        return "The mouse starved this many times: "+StarveCount+
                "\nThe mouse escaped this many times: "+EscapeCount+
                "\nThe mouse drowned this many times: "+DrownCount;
    }


   }`

这是我的第二堂课：

public class Exercise12Main {

public static void main(String[] args) throws FileNotFoundException {
    // TODO Auto-generated method stub
    Island i1 = new Island();
    i1.mouseIsland("mouseEscapeIsland-1.txt");
    System.out.println("Mouse Escape Island 1");
    System.out.println("The Coordinates of the bridges are: (0,1) & (2,11)");
    System.out.println("The Mouse is Starting at (7,6)");
    i1.moveMouse();
    i1.printStats();

}

}

这是我的岛屿：

#-##########
#----------#
#-----------
#----------#
#----------#
#----------#
#----------#
#-----X----#
#----------#
#----------#
#----------#
############

每次尝试运行此代码时，都会出现错误：线程“main”中的异常显示java.lang.NullPointerException 在Island.moveUp（Island.java:97）在Island.moveMouse（Island.java:154）在Exercise12Main.main（Exercise12Main.java:13）

Answer 1

谷歌“Java命名约定”并遵循它。

对于您的错误：您在island方法中初始化mouseIsland：

island=new char[lines1.size()][];

所以你有一个char数组的null，现在你尝试在island[0].length方法中访问moveMouse：

for(int j=0; j<island[i].length; ++j)

，您得到NullPointerException，因为island[0]是null。

如果您使用调试器，您也可以轻松找到这些错误; - ）

代码不想运行

1 个答案: