実行後にJTabbedペイントインデックスのNullpointer例外が発生する

Question

条件がtrueのときにタブ付きペインからタブを自動的に選択するコードを記述しようとしたときにエラーが発生しましたが、nullポインタ例外でエラーが発生しました私はコンパイルした後でコードを実行しようとしている間に！ 問題はloadData（）にあります。 setSelectedTab（）のメソッド。

import java.util.*; 
    import java.awt.*; 
    import javax.swing.*; 
    import java.io.*; 
    import java.awt.event.*; 
    import java.awt.event.ActionEvent; 
    import java.awt.event.ActionListener; 
    import java.awt.event.WindowListener; 

パブリッククラスGUIはJFrameのはActionListenerを実装して延び{

private static final long serialVersionUID = 1; 

ArrayList<Ship> shiplist= new ArrayList<Ship>(); 
private int shipcount = 0; 
private int index = 0; 
private Ship shipob; 
private JTextField ShipYear; 
private JTextField ShipName; 
private JTextField CrewSize; 
private JTextField ShipType; 
private JTextField NoOfPass; 
private JTextField NoOfCabins; 
private JTextField PerFull; 
private JTextField CabinRate; 
private JTextField SizeCat; 
private JTextField PerFilled; 
private JTextField LiquidType; 
private JTextField Capacity; 
private ObjectInputStream inStream; 
private ObjectOutputStream outStream; 
private JTabbedPane tab; 
private CruiseShip cruiseShip; 
private DryCargoShip dryShip; 
private LiquidCargoShip liquidShip; 
JLabel message=new JLabel(); 

パブリックGUI（） {

setSize(2000,300); 
setTitle("Ship Data"); 
Container content= getContentPane(); 
content.setBackground(Color.GRAY); 
content.setLayout(new BorderLayout()); 
JMenuBar menu=new JMenuBar(); 
JMenuItem menue= new JMenuItem("Exit"); 
menue.addActionListener(this); 
menu.add(menue); 
setJMenuBar(menu); 
this.addWindowListener(new WindowDestroyer()); 

JPanel panel1= new JPanel(); 
panel1.setBackground(Color.YELLOW); 
panel1.setLayout(new GridLayout(2,2)); 
panel1.add(new JLabel("Ship Name:")); 
ShipName= new JTextField(50); 
panel1.add(ShipName); 
panel1.add(new JLabel("Ship Year:")); 
ShipYear= new JTextField(50); 
panel1.add(ShipYear); 
panel1.add(new JLabel("Crew Size:")); 
CrewSize= new JTextField(50); 
panel1.add(CrewSize); 
panel1.add(new JLabel("Ship Type:")); 
ShipType= new JTextField(50); 
panel1.add(ShipType); 
content.add(panel1, BorderLayout.NORTH); 
JPanel panel2= new JPanel(); 
panel2.setLayout(new BorderLayout()); 
JPanel panel3= new JPanel(); 
panel3.setBackground(Color.CYAN); 
panel3.setLayout(new FlowLayout()); 
JButton Button1= new JButton("Next"); 
Button1.addActionListener(this); 
panel3.add(Button1); 
JButton Button2= new JButton("Previous"); 
Button2.addActionListener(this); 
panel3.add(Button2); 
panel2.add(panel3,BorderLayout.WEST); 
panel2.add(message,BorderLayout.EAST); 
JTabbedPane tab=new JTabbedPane(); 
content.add(panel2, BorderLayout.SOUTH); 
JPanel cs= new JPanel(); 
//JPanel z= new JPanel(); 
cs.setBackground(Color.ORANGE); 
cs.setLayout(new GridLayout(2,2)); 
cs.add(new JLabel("No of Passenger: ")); 
NoOfPass= new JTextField(25); 
cs.add(NoOfPass); 
cs.add(new JLabel("No of Cabins: ")); 
NoOfCabins= new JTextField(25); 
cs.add(NoOfCabins); 
cs.add(new JLabel("Percentage Full: ")); 
PerFull= new JTextField(25); 
cs.add(PerFull); 
cs.add(new JLabel("Cabin Rate: ")); 
CabinRate= new JTextField(25); 
cs.add(CabinRate); 
tab.addTab("Cruise Ship", cs); 
JPanel ds= new JPanel(); 
//JPanel x= new JPanel(); 
ds.setBackground(Color.ORANGE); 
ds.setLayout(new GridLayout(1,2)); 
ds.add(new JLabel("Size Category : ")); 
SizeCat= new JTextField(25); 
ds.add(SizeCat); 
ds.add(new JLabel("Percentage Filled : ")); 
PerFilled= new JTextField(25); 
ds.add(PerFilled); 
tab.addTab("Dry Cargo Ship", ds); 
JPanel ls= new JPanel(); 
//JPanel y= new JPanel(); 
ls.setBackground(Color.ORANGE); 
ls.setLayout(new GridLayout(1,2)); 
ls.add(new JLabel("Liquid Type : ")); 
LiquidType= new JTextField(25); 
ls.add(LiquidType); 
ls.add(new JLabel("Capacity : ")); 
Capacity= new JTextField(25); 
ls.add(Capacity); 
tab.addTab("Liquid Cargo Ship", ls); 
content.add(tab,BorderLayout.CENTER); 

}コンストラクタで

public static void main(String[] args) 
{ 
    GUI Gui = new GUI(); 
    Gui.readData(); 
    Gui.loadData(); 
    Gui.index = 0; 
    Gui.met(); 
    //Gui.shipcount= shiplist.size(); 
    Gui.setVisible(true); 

} 

public void actionPerformed(ActionEvent e) 
{ 
    Container container = getContentPane(); 
    String string = e.getActionCommand(); 
    if (string.equals("Next")) 
    { 
     nextShip(); 
    } 
    else if (string.equals("Previous")) 
    { 
     previousShip(); 
    } 
    else if (string.equals("Exit")) 
    { 
     writeData(); 
     System.exit(0); 
    } 
    else 
    { 
     System.out.println("Error"); 
    } 
} 

public void readData() 
{ 
    inStream=null; 
    try 
    { 
    inStream= new ObjectInputStream(new FileInputStream("shipdata.dat")); 
    try { 
     this.shipcount = 0; 
     do { 
      shiplist.add((Ship)inStream.readObject()); 
      shipcount++; 
     } while (true); 
    } 
    catch (EOFException obj1) 
    { 
     System.out.println("Entered EOF"); 
    } 
    catch (ClassNotFoundException obj2) 
    { 
     System.out.println("Class Error: " + obj2.getMessage()); 
    } 
    this.inStream.close(); 
} 
catch (FileNotFoundException obj3) 
    { 
    System.out.println("File Error: " + obj3.getMessage()); 
} 
catch (IOException obj4) 
    { 
    System.out.println("IO Error in read file data: " + obj4.getMessage()); 
} 
} 
public void met() 
{ 

    shipcount= shiplist.size(); 
} 



public void loadData() { 
     shipob = shiplist.get(index); 
     ShipName.setText(shipob.getShipName()); 
     ShipYear.setText(shipob.getYear()); 
     String a=""+shipob.getCrewSize(); 
     CrewSize.setText(a); 
     ShipType.setText(shipob.getShipType()); 
     if (shipob.getShipType().equals("Cruise Ship")) 
     { 
      System.out.println("In Cruise ship"); 
      cruiseShip = (CruiseShip)shipob; 
      String b=""+cruiseShip.getCabinRate(); 
      CabinRate.setText(b); 
      NoOfPass.setText(Integer.toString(cruiseShip.getNoOfPass())); 
      NoOfCabins.setText(Integer.toString(cruiseShip.getNoOfCabins())); 
      PerFull.setText(Double.toString(cruiseShip.getPerFull() * 100.0)); 
      tab.setSelectedIndex(0); // ERROR IN SELECT INDEX - NULL POINTER EXCEPTION 

     } 



else if (shipob.getShipType().equals("Dry Cargo Ship")) 
    { 
     System.out.println("In Dry ship"); 
     dryShip = (DryCargoShip)shipob; 
     SizeCat.setText(dryShip.getSize()); 
     String c=" "+dryShip.getPerFilled()*100.0; 
     PerFilled.setText(c); 
     try{ 
     tab.setSelectedIndex(1);} 
     catch(Exception e){ 
      System.out.println(e); 
     } 
    } 
    else if (shipob.getShipType().equals("Liquid Cargo Ship")) 
    { 
     System.out.println("In LC ship"); 
     liquidShip = (LiquidCargoShip)shipob; 
     LiquidType.setText(liquidShip.getLiqType()); 
     Capacity.setText(Integer.toString(liquidShip.getCapacity())); 
     tab.setSelectedIndex(2); 
    } 
} 




public void nextShip() { 
    if (index == shipcount - 1) { 
     message.setText("Already at last record "); 
    } 
    else { 
     message.setText(""); 
     index++; 
     loadData(); 
    } 
} 

    public void previousShip() { 
     if (index == 0) 
     { 
      message.setText("Already at first record  "); 
     } 
     else 
     { 
      message.setText(""); 
      index--; 
      loadData(); 
     } 
    } 

    public void writeData() 
    { 
     try { 
      outStream = new ObjectOutputStream(new FileOutputStream("shipdata.dat", false)); 
      for (Ship ship : shiplist) 
      { 
       outStream.writeObject(ship); 
      } 
      outStream.flush(); 
      outStream.close(); 
     } 
     catch (IOException obj1) { 
      System.out.println("IO Error in writing the data: " + obj1.getMessage()); 
     } 
    } 
    } 

Answer 1

あなたがinitializありますローカルJTabbedPaneであり、クラスで宣言され、メソッドloadDataでアクセスされているものではありません。 すなわち

、適切な方法で変数 tabを初期化してください

this.tab=new JTabbedPane(); 

代わりの

JTabbedPane tab=new JTabbedPane();