Question

为什么Eclipse不断给我构造函数的错误：

 public DenseBoard(Tile t[][]){
      Board myBoard = new DenseBoard(t.length, t[0].length);
  }

错误是：Implicit super constructor Board() is undefined. Must explicitly invoke another constructor

Class DenseBoard

package Game2048;

// Tracks the positions of an arbitrary 2D grid of Tiles.  DenseBoard
// uses an internal, multi-dimensional array to store the tiles and
// thus has a O(R * C) memory footprint (rows by columns).
public class DenseBoard extends Board {

  // Build a Board of the specified size that is empty of any tiles
  public DenseBoard(int rows, int cols){
      super(rows, cols);
  }

  // Build a board that copies the 2D array of tiles provided Tiles
  // are immutable so can be referenced without copying but the a
  // fresh copy of the 2D array must be created for internal use by
  // the Board.
  public DenseBoard(Tile t[][]){
      Board myBoard = new DenseBoard(t.length, t[0].length);
  }

班级董事会

package Game2048;

public abstract class Board{

  protected int rows;
  protected int cols;


  public Board(int rows, int cols){
      this.rows = rows;
      this.cols = cols;
  }
  // Create a distinct copy of the board including its internal tile
  // positions and any other state
  public abstract Board copy();

  // Return the number of rows in the Board
  public abstract int getRows();

  // Return the number of columns in the Board
  public abstract int getCols();

  // Return how many tiles are present in the board (non-empty spaces)
  public abstract int getTileCount();

  // Return how many free spaces are in the board
  public abstract int getFreeSpaceCount();

  // Get the tile at a particular location
  public abstract Tile tileAt(int i, int j);

  // true if the last shift operation moved any tile; false otherwise
  public abstract boolean lastShiftMovedTiles();

  // Return true if a shift left, right, up, or down would merge any
  // tiles. If no shift would cause any tiles to merge, return false.
  // The inability to merge anything is part of determining if the
  // game is over.
  public abstract boolean mergePossible();

  // Add a the given tile to the board at the "freeI"th free space.
  public abstract void addTileAtFreeSpace(int freeI, Tile tile);

  // Shift the tiles of Board in various directions.  Any tiles that
  // collide and should be merged should be changed internally in the
  // board.  Shifts only remove tiles, never add anything.  The shift
  // methods also set the state of the board internally so that a
  // subsequent call to lastShiftMovedTiles() will return true if any
  // Tile moved and false otherwise.  The methods return the score
  // that is generated from the shift which is the sum of the scores
  // all tiles merged during the shift. If no tiles are merged, the
  // return score is 0.
  public abstract int shiftLeft();
  public abstract int shiftRight();
  public abstract int shiftUp();
  public abstract int shiftDown();

}

Answer 1

我认为你想要做的就是这个

public DenseBoard(Tile t[][]){
      this(t.length, t[0].length);
 }

Answer 2

只是指出

public DenseBoard(Tile t[][]) {
    Board myBoard = new DenseBoard(t.length, t[0].length);
}

myBoard是局部变量，在使用new DenseBoard(Tile t[][])创建新对象时，您将无法引用它。

你可以通过两种方式完成。

public DenseBoard(Tile t[][]) {
    super(t.length, t[0].length); // calling super class constructor
}

// or
// I would prefer this
public DenseBoard(Tile t[][]) {
    this(t.length, t[0].length); // calling DenseBoard(int rows, int cols) constuctor, which is internally passing the value to super class.
}

Answer 3

在您的班级Board中，您只有一个构造函数需要2 int个参数。

由于DenseBoard扩展Board，DenseBoard中的每个构造函数都应调用Board中的一些构造函数。

如果Board有一个no-arg构造函数，编译器会自动为你调用它。但是由于你没有，你应该从你的public DenseBoard(Tile t[][])明确地调用另一个构造函数。

Answer 4

您的构造函数需要调用超类的构造函数。如果超类定义了无参数构造函数，则不会看到此错误。要使用某些代码扩展其他答案，您需要的是

 public DenseBoard(Tile t[][]){
      //You need a way to figure meaningful values to the superconstructor here
      super(intVar1, intVar2);
      Board myBoard = new DenseBoard(t.length, t[0].length); //I think 
     //this now becomes unnecessary?
  }

或者修改您的Board课程以包含

public Board()
{
...
}

Answer 5

您可以这样做将值发送到父类。

public DenseBoard(Tile t[][]){
      super(t.length, t[0].length);
 }

Answer 6

我认为你的DenseBoard类应该实现所有Board类的抽象方法。像这样：

package Game2048;
public class DenseBoard extends Board {

  public DenseBoard(int rows, int cols){
      super(rows, cols);
  }

  public DenseBoard(Tile t[][]){
      Board myBoard = new DenseBoard(t.length, t[0].length);
  }

  public Board copy(){

  }

  public int getRows(){

  }

  public int getCols(){

  }

  public int getTileCount(){

  }

  public int getFreeSpaceCount(){

  }

  public Tile tileAt(int i, int j){

  }

  public boolean lastShiftMovedTiles(){

  }

  public boolean mergePossible(){

  }

  public void addTileAtFreeSpace(int freeI, Tile tile){

  }

  public int shiftLeft(){

  }

  public int shiftRight(){

  }

  public int shiftUp(){

  }

  public int shiftDown(){

  }
}

必须显式调用另一个构造函数

6 个答案: