我正在尝试将船放在基于控制台的棋盘游戏上，我有以下错误，不知道如何调试它们。
线程“main”java.lang.NullPointerException中的异常 at NavalBattle.Board.print（Board.java:570） at NavalBattle.Board.placeShipsP1（Board.java:267） 在NavalBattle.Board。（Board.java:61） at NavalBattle.Controller.start（Controller.java:29） 在NavalBattle.Controller.main（Controller.java:21）
第570行是value = this.ships2 [row] [col] .toString（）;
import java.util.Scanner;
public class Controller {
/**
* The board that represents the current state of the game.
*/
private Board board;
public Controller() {}
/**
* This creates one Library object and calls its start method.
*
* @Param args
*/
public static void main(String[] args) {
new Controller().start();
}
int PL;
/**
* The PLrimary method that starts and coordinates a game. Call this to
* begin a new game.
*/
public void start() {
this.board = new Board();
Scanner scanner = new Scanner(System.in);
this.board.moveShip();
while (!this.board.isGameOver()) {
PL = 1;
this.board.moveShip();
PL = 2;
this.board.moveShip2(null);
this.board.remap();
this.board.moveShip2(null);
System.out.println("Enter a row and column number at which to shoot (e.g., 2,3): ");
String[] coordinates = scanner.nextLine().split(",");
if (coordinates.length != 2) {
System.out.println("PLlease enter coordinates in the correct format.");
continue;
}
int row = Integer.parseInt(coordinates[0].trim());
int column = Integer.parseInt(coordinates[1].trim());
this.board.bombOp(row, column);
}
if (PL == 1);{
System.out.println("Game Over Player 2 wins");
}
if (PL == 2){
System.out.println("Game Over Player 1 wins");
}
}
}
// Board Class
import java.util.ArrayList;
import java.util.Scanner;
public class Board {
int x = 0;
int y = 0;
ArrayList<Ships> player1 = new ArrayList<>();
ArrayList<Ships> player2 = new ArrayList<>();
/**
* The number of shots that have hit ships
*/
private int hitCount;
/**
* Track the locations of the board that have been fired upon
*/
private boolean[][] locationsFiredUpon;
/**
* Track the ships in the game
*/
private Ships[][] ships;
private Ships[][] ships2;
private Ships[][] shipsM;
/**
* The number of ships sunk
*/
private int shipsSunk;
/**
* The number of shots fired
*/
private int shotsFired;
/**
* Constructor. Initializes internal counters and populates the game
* board with randomly placed ships.
*/
public Board() {
this.hitCount = 0;
this.shipsSunk = 0;
this.shotsFired = 0;
board();
this.ships = new Ships[6][9];
this.ships2 = new Ships[6][9];
this.locationsFiredUpon = new boolean[6][9];
for (int row=0; row < this.ships.length; row++) {
for (int col=0; col < this.ships[row].length; col++) {
this.ships[row][col] = new Conflict();
this.locationsFiredUpon[row][col] = false;
}
}
this.placeShipsP1();
this.placeShipsP2();
this.moveShip();
this.moveShip2(player1);
}
public void remap() {
board();
this.locationsFiredUpon = new boolean[6][9];
for (int row=0; row < this.ships.length; row++) {
for (int col=0; col < this.ships[row].length; col++) {
this.ships[row][col] = new Conflict();
this.locationsFiredUpon[row][col] = false;
}
}
}
/**
* Constructor for testing. Accepts an input ship array and does not
* attempt to place ships
* @param shipArray
*/
public Board(Ships[][] shipArray) {
this.hitCount = 0;
this.shipsSunk = 0;
this.shotsFired = 0;
this.ships = shipArray;
this.locationsFiredUpon = new boolean[6][9];
for (int row=0; row < this.ships.length; row++) {
for (int col=0; col < this.ships[row].length; col++) {
this.locationsFiredUpon[row][col] = false;
}
}
}
public void board(){
this.ships = new Ships[6][9];
this.ships2 = new Ships[6][9];
}
/**
* Get the number of shots fired that have hit a ship.
* @return The number of shots fired that have hit a ship
*/
public int getHitCount() {
return this.hitCount;
}
/**
* Get the game board.
* @return A 2-D array of Ships representing the game
*/
public Ships[][] getShipArray() {
return this.ships;
}
public Ships[][] getShipArray2() {
return this.ships2;
}
/**
* Get the number of ships sunk.
* @return The number of ships sunk
*/
public int getShipsSunk() {
return this.shipsSunk;
}
/**
* Get the number of shots fired so far.
* @return The number of shots fired
*/
public int getShotsFired() {
return this.shotsFired;
}
/**
* Create an list of ships that can be placed on the board:
* - 1 battleship
* - 2 cruisers
* - 3 destroyers
* - 4 submarines
* @return ships to be placed on the board
*/
private ArrayList<Ships> generateInitialShipArrayList1() {
ArrayList<Ships> ship = new ArrayList<Ships>();
for (int i=0; i<1; i++) {
ship.add(new Battleship());
}
for (int i=0; i<0; i++) {
ship.add(new Minesweeper());
}
for (int i=0; i<0; i++) {
ship.add(new Destroyer());
}
for (int i=0; i<0; i++) {
ship.add(new Submarine());
}
for (int i=0; i<0; i++) {
ship.add(new Mines());
}
return ship;
}
private ArrayList<Ships> generateInitialShipArrayList2() {
ArrayList<Ships> ship2 = new ArrayList<Ships>();
for (int i=1; i<2; i++) {
ship2.add(new Battleship());
}
for (int i=1; i<1; i++) {
ship2.add(new Minesweeper());
}
for (int i=1; i<1; i++) {
ship2.add(new Destroyer());
}
for (int i=1; i<1; i++) {
ship2.add(new Submarine());
}
for (int i=1; i<1; i++) {
ship2.add(new Mines());
}
return ship2;
}
/**
* Indicate whether the game is over by checking if all ships have been
* sunk.
* @return true if all ships are sunk; otherwise false
*/
public boolean isGameOver() {
return (this.shipsSunk == 1);
}
/**
* Whether the specified position is occupied by a ship and is not empty
* sea.
* @param row
* @param column
* @return true if the position has a ship; else false
*/
public boolean isOccupied(int row, int column) {
System.out.println("Occupardo, you no go here");
return !(this.ships[row][column] instanceof Conflict);
}
public void placeShipsP1() {
System.out.println("");
print();
ArrayList<Ships> shipsToMove = this.generateInitialShipArrayList1();
player1 = this.generateInitialShipArrayList1();
boolean okToPlaceShipHere = false;
int row = 0;
int column = 0;
String Tp = "1";
boolean horizontal = false;
if(okToPlaceShipHere = false){
System.out.println("Occupardo, you no go here");
}
for (Ships ship : player1) {
while (!okToPlaceShipHere) {
Scanner scanner = new Scanner( System.in );
System.out.println("player1 enter a row and column (e.g., 2,3)");
System.out.println("please enter the row of " + ship.getShipType());
String[] coordinates = scanner.nextLine().split(",");
if (coordinates.length != 2) {
System.out.println("Please enter coordinates in the correct format.");
continue;
}
row = Integer.parseInt(coordinates[0].trim());
column = Integer.parseInt(coordinates[1].trim());
ship.setX(row);
ship.setY(column);
System.out.println(ship.getX() + " " + ship.getY());
// row = Random.nextInt(6);
// column = Random.nextInt(9);
horizontal = true;
okToPlaceShipHere = ship.okToPlaceShipAt(row, column, horizontal, this);
}
if( okToPlaceShipHere = true){
this.bombOp(row, column);
}
ship.setBowColumn(column);
ship.setBowRow(row);
ship.setPlayer(Tp);
ship.setX(row);
ship.setY(column);
System.out.println(ship.getX() + " " + ship.getY() + " " + ship.getPlayer());
ship.setHorizontal(horizontal);
this.placeShipIntoShipsArray(ship);
okToPlaceShipHere = false;
System.out.println("");
print();
}
}
public void placeShipsP2() {
System.out.println("");
print();
ArrayList<Ships> shipsToPlace = this.generateInitialShipArrayList1();
player2 = this.generateInitialShipArrayList2();
boolean okToPlaceShipHere = false;
int row = 0;
int column = 0;
String Tp = "2";
boolean horizontal = false;
if(okToPlaceShipHere = false){
System.out.println("Occupardo, you no go here");
}
for (Ships ship : player2) {
while (!okToPlaceShipHere) {
Scanner scanner = new Scanner( System.in );
System.out.println("Player 2 enter a row and column (e.g., 2,3)");
System.out.println("please enter the row of " + ship.getShipType());
String[] coordinates = scanner.nextLine().split(",");
if (coordinates.length != 2) {
System.out.println("Please enter coordinates in the correct format.");
continue;
}
row = Integer.parseInt(coordinates[0].trim());
column = Integer.parseInt(coordinates[1].trim());
ship.setX(row);
ship.setY(column);
System.out.println(ship.getX() + " " + ship.getY());
// row = random.nextInt(6);
// column = random.nextInt(9);
horizontal = true;
okToPlaceShipHere = ship.okToPlaceShipAt(row, column, horizontal, this);
}
ship.setBowColumn(column);
ship.setBowRow(row);
ship.setPlayer(Tp);
ship.setX(row);
ship.setY(column);
System.out.println(ship.getX() + " " + ship.getY() + " " + ship.getPlayer());
ship.setHorizontal(horizontal);
this.placeShipIntoShipsArray(ship);
okToPlaceShipHere = false;
System.out.println("");
print();
}
}
/**
* Place the given ship into locations in the
* 2Darray that tracks ship positions.
* @param ship
*/
private void placeShipIntoShipsArray(Ships ship) {
int row = ship.getBowRow();
int column = ship.getBowColumn();
// player1.add.ship;
player1.removeAll(player1);
player2.removeAll(player2);
if (ship.isHorizontal()) {
for (int i=0; i < ship.getLength(); i++) {
this.ships[row][(column+i)] = ship;
}
}
else {
for (int i=0; i < ship.getLength(); i++) {
this.ships[(row+i)][column] = ship;
}
}
}
public void ifship(){
for (int i=0; i < 1; i++){
board();
}
}
private void placeShipIntoShipsArray2(Ships ship) {
int row = ship.getBowRow();
int column = ship.getBowColumn();
//player1.add.ships;
player1.removeAll(player1);
player2.removeAll(player2);
//ship.clear();
if (ship.isHorizontal()) {
for (int i=0; i < ship.getLength(); i++) {
this.ships2[row][(column+i)] = ship;
}
}
else {
for (int i=0; i < ship.getLength(); i++) {
this.ships2[(row+i)][column] = ship;
}
}
}
public void display() {
System.out.print(" ");
for (int i=0; i < 9; i++) {
System.out.print(i + " ");
}
System.out.print("\n");
for (int row=0; row < 6; row++) {
System.out.print(" " + row + " ");
for (int col=0; col < 9; col++) {
String value = "";
if (this.locationsFiredUpon[row][col]) {
value = "-";
}
if (this.ships2[row][col] != null) {
value = this.ships2[row][col].toString() ;
}
else {
value = "-";
}
System.out.print(value + " ");
}
System.out.print("\n");
}
remap();
}
boolean pr = false;
boolean pr2 = false;
public void moveShip(){
System.out.println("So you wanna move a ship");
System.out.println(player1);
for (int i=0; i > 1; i++) {
print();
System.out.println("map 1");
pr = true;
}
if (pr = true){
display();
}
//ArrayList<Ships> shipsToMove = new ArrayList<>();
ArrayList<Ships> shipsToMove = new ArrayList<>();
ArrayList<Ships> shipsToMove1 = player1;
boolean notMoved = false;
int rowM = 0;
int columnM = 0;
String Tp = "1";
boolean horizontal = false;
if(notMoved = false){
System.out.println("Occupardo, you no go here");
}
System.out.println("gets here 1");
for (Ships shipM : shipsToMove1) {
System.out.println("gets here 2");
while (!notMoved) {
Scanner scanner1 = new Scanner( System.in );
System.out.println("Enter a area to move to (e.g., 2,3)");
System.out.println("please enter a movement for the: " + shipM.getShipType() + shipM.getBowRow());
String[] coordinates = scanner1.nextLine().split(",");
if (coordinates.length != 2) {
System.out.println("Please enter coordinates in the correct format.");
continue;
}
rowM = Integer.parseInt(coordinates[0].trim());
columnM = Integer.parseInt(coordinates[1].trim());
// row = random.nextInt(6);
// column = random.nextInt(9);
horizontal = true;
notMoved = shipM.okToPlaceShipAt(rowM, columnM, horizontal, this);
}
if( notMoved = true){
this.bombOp(rowM, columnM);
}
shipM.setBowColumn(columnM);
shipM.setBowRow(rowM);
shipM.setHorizontal(horizontal);
this.placeShipIntoShipsArray2(shipM);
notMoved = false;
System.out.println("");
display();
}
}
public void moveShip2(ArrayList<Ships> player2){
System.out.println("So you wanna move a ship");
for (int i=0; i > 1; i++) {
display();
pr2 = true;
}
if (pr2 = true){
display();
}
ArrayList<Ships> shipsToMove = new ArrayList<>();
player2 = this.player2;
boolean notMoved = false;
int rowM = 0;
int columnM = 0;
String Tp = "1";
boolean horizontal = false;
if(notMoved = false){
System.out.println("Occupardo, you no go here");
}
System.out.println("gets here 1");
for (Ships ship : player2) {
System.out.println("gets here 2");
while (!notMoved) {
Scanner scanner1 = new Scanner( System.in );
System.out.println("Enter a area to move to (e.g., 2,3)");
System.out.println("please enter a movement for the: " + ship.getShipType());
String[] coordinates = scanner1.nextLine().split(",");
if (coordinates.length != 2) {
System.out.println("Please enter coordinates in the correct format.");
continue;
}
rowM = Integer.parseInt(coordinates[0].trim());
columnM = Integer.parseInt(coordinates[1].trim());
// row = random.nextInt(6);
// column = random.nextInt(9);
horizontal = true;
notMoved = ship.okToPlaceShipAt(rowM, columnM, horizontal, this);
}
if( notMoved = true){
this.bombOp(rowM, columnM);
}
ship.setBowColumn(columnM);
ship.setBowRow(rowM);
ship.setHorizontal(horizontal);
this.placeShipIntoShipsArray2(ship);
notMoved = false;
System.out.println("");
display();
display();
}
}
/**
* Print the current state of the game.
*/
public void print() {
System.out.print(" ");
for (int i=0; i < 9; i++) {
System.out.print(i + " ");
}
System.out.print("\n");
for (int row=0; row < 6; row++) {
System.out.print(" " + row + " ");
for (int col=0; col < 9; col++) {
String value = "";
if (this.locationsFiredUpon[row][col]) {
value = "-";
}
**if (this.ships[row][col] != null) {
value = this.ships[row][col].toString() ;**
}
if (this.locationsFiredUpon[row][col]) {
value = this.ships2[row][col].toString();
}
if (this.ships2[row][col] != null) {
value = this.ships2[row][col].toString() ;
}
else {
value = "-";
}
System.out.print(value + " ");
}
System.out.print("\n");
}
}
public void print2() {
System.out.print(" ");
for (int i=0; i < 9; i++) {
System.out.print(i + " ");
}
System.out.print("\n");
for (int row=0; row < 6; row++) {
System.out.print(" " + row + " ");
for (int col=0; col < 9; col++) {
String value = "";
if (this.locationsFiredUpon[row][col]) {
value = "-";
}
if (this.shipsM[row][col] != null) {
value = this.shipsM[row][col].toString() ;
}
if (this.locationsFiredUpon[row][col]) {
value = this.ships2[row][col].toString();
}
if (this.ships2[row][col] != null) {
value = this.ships2[row][col].toString() ;
}
else {
value = "-";
}
System.out.print(value + " ");
}
System.out.print("\n");
}
board();
}
/**
* Handle a shot fired at the specified position.
* @param row
* @param column
* @return true if a ship was hit; else false
*/
public boolean bombOp(int row, int column) {
this.shotsFired++;
this.locationsFiredUpon[row][column] = true;
Ships shipAtLocation = this.ships[row][column];
if (shipAtLocation.isSunk()) {
return false;
}
boolean shipWasHit = shipAtLocation.bombOp(row, column);
if (shipWasHit) {
this.hitCount++;
}
if (shipAtLocation instanceof Conflict) {
return shipWasHit;
}
if (shipAtLocation.isSunk()) {
shipsSunk++;
}
return shipWasHit;
}
答案 0 :(得分：4)
调试NullPointerException的最佳方法是查看堆栈跟踪的第一行，即：
NavalBattle.Board.print(Board.java:570)
这意味着错误发生在Board.java文件中的第570行。您应该转到文件中的这一行，并查看该行上哪些变量为空。
第570行是value = this.ships2[row][col].toString();。在这一行上，只有3件事可能为空：
this.ships2 如果您无法立即看到哪些是null，请使用IDE在那里设置断点并以调试模式启动程序。当IDE停在该行时，为上述3个表达式中的每个表达式创建一个“监视表达式”，或使用“计算表达式”功能。其中一个应为null。
没有调试，我只能猜测，但我想我可以做出很好的猜测。 this.ship2不太可能为null，因为我可以看到您已在代码中初始化它。我也不认为this.ships2 [row]为null - 我认为你在构造函数中正确初始化了2D数组。因此，我认为this.ships2 [row] [col]为null，并且在null上调用toString（）会抛出NPE。为了证实我的理论，您可以用以下代码替换该行：
value = String.valueOf(this.ships2[row][col]);