java 2d数组没有正确填充

问题描述：

概述：我有一个“节点”的二维数组，它是一个简单的对象，我有一个x和y坐标并存储一些基本值。java 2d数组没有正确填充

网格是一个类，它将所有节点保存在其二维节点数组“节点”中。网格构造函数需要两个参数：宽度和高度（x & y），然后使用坐标（字段）与二维数组中的坐标相匹配的节点填充二维数组，除了这样做以外。出于某种原因，该阵列空物体填满，并抛出一个NullPointerException每当我试图全球化志愿服务青年它们

public class Node { 

//fields 

public int x, y; //coordinates 
public int Fcost, Hcost; //values used for pathfinding. f is distance from user, h is distance from target. 
public boolean validity = false; 

//Constructors 
public Node(int x, int y) { 
    this.x = x; 
    this.y = y; 
} 

public Node(int x, int y, int F, int H) { 
    this.x = x; 
    this.y = y; 
    this.Fcost = F; 
    this.Hcost = H; 
} 

public Node(Node n) { 
    this.x = n.x; 
    this.y = n.y; 
    this.Fcost = n.Fcost; 
    this.Hcost = n.Hcost; 
} 



public boolean isValid() { 
    ////if out of bounds, return flase. 
    if (this.x >= Game.width) { 
     return false; 
    } 
    if (this.x < 0) { 
     return false; 
    } 
    if (this.y >= Game.height) { 
     return false; 
    } 
    if (this.y < 0) { 
     return false; 
    } 

    return true; 
} 

public void checkIfValid() { 
    this.validity = this.isValid(); 
}

public class Grid { 

public Node[][] nodes; 
private int length, height; 

///constructor 
//populates the grid with a new node for each coordinate 
public Grid(int x, int y) { 
    nodes = new Node[x + 1][y + 1]; 
    for (int i = 0; i < x; i++) { 
     for (int w = 0; w < y; w++) { 
      nodes[x][y] = new Node(x, y); 
      System.out.println("populating..."); 
     } 
    } 
    this.length = x; 
    this.height = y; 

    ////prints the number of nodes 
    int w = 0; 
    for (Node[] a : nodes) { 
     for (Node n : a) { 
      w++; 
     } 
    } 
    System.out.println("nodes " + w); 
} 

///methods 
public Node[] getNeighbors(Node in) { 
    ArrayList<Node> n = new ArrayList<>(); 

////NOT YET IMPLEMENTED 
    return (Node[]) n.toArray(); 
} 

///tells each node to check weather or not it is valid 
public void update() { 
    for (Node n[] : nodes) { 
     for (Node realNode : n) { 
      realNode.checkIfValid(); 
     } 
    } 
} 

}

编辑 - 这里是打印出来。游戏是为其网格调用“更新”方法的类。

java.lang.NullPointerException 
at Pathfinding.Grid.update(Grid.java:55) 
at pkg2dgame.Game.tick(Game.java:62) 
at pkg2dgame.Game.run(Game.java:104) 
at java.lang.Thread.run(Thread.java:745)

你能告诉我们的错误消息，从控制台得到什么？ –

你正在迭代我和w，但你总是分配给同一个节点（nodes [x] [y]应该是nodes [i] [w]？） – HomeIsWhereThePcIs

答

nodes[x][y] = new Node(x, y);应该nodes[i][w] = new Node(x, y);

您再植相同的索引所有的时间，由于所有的阵列桶是空的。您的代码还有一个问题是，for循环不会循环到2d数组的末尾。

for (int i = 0; i < nodes.length; i++) { 
     for (int w = 0; w < nodes[i].length; w++) { 
      nodes[i][w] = new Node(x, y); 
      System.out.println("populating..."); 
     } 
}

正在对null值执行操作时抛出该错误。

非常感谢你。完美的作品 – joey101937

答

填充节点正确

for (int i = 0; i < x; i++) { 
     for (int w = 0; w < y; w++) { 
      nodes[i][w] = new Node(i, w); 
      System.out.println("populating..."); 
     } 
    }

java 2d数组没有正确填充

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