Java 枚举静态方法引发空指针异常
我试着用复合框和一组数字拼凑出一个数独游戏。我有这样的想法: 数独游戏 数独盒子 数独数字Java 枚举静态方法引发空指针异常,java,enums,nullpointerexception,Java,Enums,Nullpointerexception,我试着用复合框和一组数字拼凑出一个数独游戏。我有这样的想法: 数独游戏 数独盒子 数独数字 NullPointerException被抛出到SudokuPuzzle.setDigit()。课程中不相关的部分在这里被剥离。为什么会引发这样的异常?类SudokuPuzzle{ class SudokuPuzzle { SudokuBox[][] grid=new SudokuBox[3][3]; // here you have to assign `SudokuBox` references
NullPointerException
被抛出到SudokuPuzzle.setDigit()
。课程中不相关的部分在这里被剥离。为什么会引发这样的异常?类SudokuPuzzle{
class SudokuPuzzle {
SudokuBox[][] grid=new SudokuBox[3][3];
// here you have to assign `SudokuBox` references to your array array
for(int i=0;i<3;i++){
for(int j=0;j<3;j++){
grid[i][j] = new SudokuBox();
}
}
public void setDigit(int row,int col,int digit) {
SudokuDigit a=SudokuDigit.SudokuDigitfromInt(digit);
grid[row/3][col/3].setDigit(row%3,col%3,a);
}
}
SudokuBox[][]网格=新的SudokuBox[3][3];
//在这里,您必须为数组分配'SudokuBox'引用
对于(int i=0;i您需要在数组的实例之后再实例数组的每个元素:
SudokuBox[][] grid=new SudokuBox[3][3];
for(int y=0; y<3; y++) {
for(int x=0; x<3; x++) {
grid[y][x] = new SudokuBox();
}
}
SudokuBox[][]网格=新的SudokuBox[3][3];
对于(int y=0;ySudokuBox[]]grid=new SudokuBox[3][3];
每个引用仍然是null
。您需要初始化每个引用。grid[row/3][col col/3]=new SudokuBox();grid[row/3][col col 3]。设置位数(row%3,col 3,a);
enum SudokuDigit {
one,two,three,four,five,six,seven,eight,nine;
public static SudokuDigit SudokuDigitfromInt(int digit) {
switch(digit) {
case 1: return one;
case 2: return two;
case 3: return three;
case 4: return four;
case 5: return five;
case 6: return six;
case 7: return seven;
case 8: return eight;
case 9: default: return nine;
}
}
public static int IntfromSudokuDigit(SudokuDigit digit) {
switch(digit) {
case one: return 1;
case two: return 2;
case three: return 3;
case four: return 4;
case five: return 5;
case six: return 6;
case seven: return 7;
case eight: return 8;
case nine: default: return 9;
}
}
}
class SudokuPuzzle {
SudokuBox[][] grid=new SudokuBox[3][3];
// here you have to assign `SudokuBox` references to your array array
for(int i=0;i<3;i++){
for(int j=0;j<3;j++){
grid[i][j] = new SudokuBox();
}
}
public void setDigit(int row,int col,int digit) {
SudokuDigit a=SudokuDigit.SudokuDigitfromInt(digit);
grid[row/3][col/3].setDigit(row%3,col%3,a);
}
}
SudokuBox[][] grid=new SudokuBox[3][3];
for(int y=0; y<3; y++) {
for(int x=0; x<3; x++) {
grid[y][x] = new SudokuBox();
}
}