如何用用戶定義的對象填充數組？

Question

我正在編寫一個程序，該程序創建一個 object（線），其中包含一個名稱和兩個節點（x、y、z 坐標），然后將其存儲在單獨的 object（類 LineModel）中。 在 class LineModel 中，創建了一個方法 getNodes()，它應該返回一個包含所有節點的數組。

我的問題出在方法 getNodes() 中，因為我正在努力填充數組。 我的代碼如下。

public class LineModel {

    // Object attributes
    private String name;
    private Line[] lines;
    private int numLines;

    // Constructor
    public LineModel(String name, int maxLines) {
        this.name = name;
        lines = new Line[maxLines];
        numLines = 0;
    }

    public void addLine(Line line) {
        if (contains(line)) {
            System.out.println("Line " + line.getName() + " already in model");
            return;
        }
        if (numLines < lines.length) {
            lines[numLines] = line;
            numLines++;
        } else {
            System.out.println("Increase lines array size.");
            System.exit(1);
        }
    }

    public boolean contains(Line line) {
        for (int i = 0; i < numLines; i++) {
            if (line == lines[i])
                return true;
        }
        return false;
    }

    public Line getLine(String name) {
        for (int i = 0; i < numLines; i++) {
            if (lines[i].getName().equals(name))
                return lines[i];
        }
        System.out.println("Line " + name + " not found");
        return null;
    }

    public void printModel() {
        System.out.println('\n' + "Line model: " + name);
        for (int i = 0; i < numLines; i++) {
            System.out.println(lines[i]);
        }
    }

    public Node getNode(String name) {
        // Loop through lines
        for (int i = 0; i <= numLines; i++) {
            // Check if node 1 is contained in the line and returns if true
            if (lines[i].getN1().getName().equals(name)) {
                return lines[i].getN1();
            }
            // Check if node 2 is contained in the line and returns if true
            else if (lines[i].getN2().getName().equals(name)) {
                return lines[i].getN2();
            }
        }
        return null;
    }

    public Node[] getNodes() {
        Node[] nodes = new Node[2 * numLines];
        for (int i = 0; i < numLines; i++) {
            Node start = lines[i].getN1();
            Node end = lines[i].getN2();
            for (int j = 0; j < nodes.length - 1; j++) {
                nodes[j] = start;
                for (int k = 1; k <= nodes.length - 1; k++) {
                    nodes[k] = end;
                }
            }
        }
        return nodes;
    }
}

類節點和線在下面

public class Node {
    // Object attributes
    private String name;
    private double[] coordinates;

    // Constructor(s)
    public Node(String name, double x) {
        this.name = name;
        coordinates = new double[1];
        coordinates[0] = x;
    }

    public Node(String name, double x, double y) {
        this.name = name;
        coordinates = new double[2];
        coordinates[0] = x; coordinates[1] = y;
    }

    public Node(String name, double x, double y, double z) {
        this.name = name;
        coordinates = new double[3];
        coordinates[0] = x; coordinates[1] = y; coordinates[2] = z;
    }

    // Object methods
    public String getName(){
        return name;
    }
    
    public double[] getCoordinates(){
        return coordinates;
    }
    
    public double getX() {
        if (coordinates.length > 0){
            return coordinates[0];
        } else {
            return Double.NaN;
        }
    }
    
    public double getY() {
        if (coordinates.length > 1){
            return coordinates[1];
        } else {
            return Double.NaN;
        }
    }
    
    public double getZ() {
        if (coordinates.length > 2){
            return coordinates[2];
        } else {
            return Double.NaN;
        }
    }

    public String toString() {
        return "Node "+name+" "+Arrays.toString(coordinates);
    }
}

public class Line {
    // Object attributes
    private String name;
    private Node n1, n2;
    
    // Constructor(s)
    public Line(String name, Node n1, Node n2){
        this.name = name;
        this.n1 = n1;
        this.n2 = n2;
    }
    
    public String getName(){ return name; }
    
    // Object methods
    public double length(){
        double[] n1C = n1.getCoordinates();
        double[] n2C = n2.getCoordinates();
        if(n1C.length == n2C.length){
            double pythagoras = 0;
            for (int i = 0; i < n1C.length; i++) {
                double dv = n2C[i] - n1C[i];
                pythagoras += dv*dv;
            }
            return Math.sqrt(pythagoras);
        }
        return Double.NaN;
    }

    @Override
    public String toString(){
        return "Line "+name+" "+n1.getName()+"-->"+n2.getName()+" Length = "+length();
    }

我現在的output是這樣的：

[L_22751459.Node;@7530d0a

Answer 1

你只需要用下面的代碼替換你的 getNodes() 方法。

需要引入額外的變量 count 並且對於每個添加的節點只需增加它。 所以自動為兩行添加四個節點，如node[0],node[1],node[2],node[3]

public Node[] getNodes() {
        int count=0;
        Node[] nodes = new Node[2 * numLines];
        for (int i = 0; i < numLines; i++) {
            nodes[count]=lines[i].getN1();
            nodes[count+1]=lines[i].getN2();
            count=count+2;
        }
        return nodes;
    }



public static void main(String[] args) {
    LineModel obj2=new LineModel("l2",2);
    obj2.addLine(new Line("name1",new Node("x",1.0),new Node("y",2.0)));
    obj2.addLine(new Line("name2",new Node("x",2.0),new Node("y",3.0)));
    Node[] arr=obj2.getNodes();
    Arrays.stream(arr).forEach(node -> System.out.println(node.toString()));
}

上面的代碼打印在 Output 下面，這是非常好的。

Node x [1.0]
Node y [2.0]
Node x [2.0]
Node y [3.0]