Question

我不是很擅长OOP，我遇到了这个问题，构造函数没有返回任何东西。

public class CrossEntropy extends Thread{

    protected CEMobileAgentMigrationPlan appOwner;
    private SensorNode[] sensorNodes;
    private JLabel status;
    private JTextArea textArea;
    Integer temp = null;
    boolean first=true;
    int tempor;
    int populasi=1000;
    double a = 0.8;
    double g=(int)(populasi/3);
    int max=appOwner.sensorCount+populasi;
    private double costa=0;
    private int[] samatidak;
    public int[] mem;
    private double[] sortbox;    
    private double w[][]  = new double[max][max];
    private double p[][]  = new double[max][max];
    private double[][] pn;
    private int[][] jalur;
    private double[] cost;
    boolean first2;

    public CrossEntropy(CEMobileAgentMigrationPlan appOwner){
        System.out.println("hi !");
        this.appOwner=appOwner;
        System.out.println("hi hi hello !");
        this.sensorNodes=appOwner.sensorNodeList;
        System.out.println("hello !");
    }

    //method shortened

    public void run(){//engga kepanggil
        System.out.println("Testtament");
        double time = System.currentTimeMillis();
        double thisCost = 0.0;
        double oldCost = 0.0;
        int countSame=0;
        int duration=0;
        double hasilakhir =0;
        boolean cek = false;
        //matrikRate();
        while (countSame<1000){
            membangkitkanTour();
            getCost();
            thisCost = costa;
            if (cek==false){
               oldCost=thisCost;
               cek=true;
            }
            if (thisCost<oldCost){
                 oldCost=thisCost;
                 costa=0;
                 getCost();
                 hasilakhir=costa;
                 countSame=0;

            }else{
                 countSame++;
                 //appOwner.paint();
            }
            costa=0;
        }
        duration = (int) (System.currentTimeMillis()-time);
        StringBuffer sb = new StringBuffer();
        for (int i=0; i< appOwner.sensorCount; i++){
            sb.append("Node Address: " + appOwner.sensorNodeList[mem[i]].getAddress());
            sb.append(" RSSI: " + appOwner.sensorNodeList[mem[i]].getSignalStrength());
            sb.append(" Battery Level: " + appOwner.sensorNodeList[mem[i]].getRemainingBattery());
            sb.append("\n");
        }

       String status = "CE finds Solution after " + duration + " ms with max rating= " + hasilakhir;
       String migrationInfo = sb.toString();
       appOwner.setStatus(status, "Urutan Rute Migrasi: \n" + migrationInfo);

    }

}

这是我想要调用构造函数的类

public class CEMobileAgentMigrationPlan extends JFrame {
    //protected SensorNodePlacementMap map = null;
    SensorNode[] sensorNodeList;
    CrossEntropy worker;
    private JTextArea textArea;
    boolean started = false;
    private JLabel status;
    int sensorCount;

    public CEMobileAgentMigrationPlan(){
        getContentPane().setLayout(new BorderLayout());
        status = new JLabel("Starting App...");
        textArea = new JTextArea("Listening... \b");
        getContentPane().add(status,BorderLayout.SOUTH);
        getContentPane().add(textArea,BorderLayout.CENTER);
        setSize(500,400);
        setTitle("Cross Entropy for Mobile Agent Itinerary Planning");
        this.setResizable(true);
        setVisible(true);
    }

    public void setSensorNodes(SensorNode[] sensorNodes){
        this.sensorNodeList = sensorNodes;
        this.sensorCount = this.sensorNodeList.length;
    }

    public int getSensorCount(){
        return sensorCount;
    }

    public SensorNode[] getSensorNodeList(){
        return sensorNodeList;
    }

    public void setStatus(String statusTxt, String migrationInfo){
        status.setText(statusTxt);
        textArea.setText(migrationInfo);
    }

    public void setSensorNodeList(SensorNode[] sensorNodeList) {
        this.sensorNodeList = sensorNodeList;
    }

    public void start(){ // yang ini tidak bisa
        this.started=true;
        //map.update(map.getGraphics());
        //if (worker!= null)worker=null;
        System.out.println("lol");
        worker = new CrossEntropy(this); <<<<< this is the troublemaker
        System.out.println("lol1111");
        worker.setPriority(Thread.MIN_PRIORITY);
        //map.update(map.getGraphics());
        worker.start();
    }


}

我已经做了一些类似的课程，找出原因，但我找不到:(

Answer 1

如果您提供的代码示例已完成，那么在尝试构造对象时，您将获得NullPointerException。这条线

int max=appOwner.sensorCount+populasi;

会导致它，因为构造对象时appOwner为null。在调用构造函数之前初始化属性。你应该在construtor本身计算这个值，例如

int max;

public CrossEntropy(CEMobileAgentMigrationPlan appOwner){
    System.out.println("hi !");
    this.appOwner=appOwner;
    max=appOwner.sensorCount+populasi;
    System.out.println("hi hi hello !");
    this.sensorNodes=appOwner.sensorNodeList;
    System.out.println("hello !");
}

Java构造函数永远不会完成构建

1 个答案: