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Why do I have a NullPointerException here?

I created a class whose name is Manager, and I have a Frame whose name is BirthList, and this frame has a table. I work with MySQL and I entered some data into the “parent table” in MySQL. And I want to add this data from the MySQL table to the table that is in my frame. TIP: birthList - list of birth objects. but I will find this exception, why? Please help me: (

Manager Class:

  public Manager class{
  Logger logger = Logger.getLogger(this.getClass().getName());
  private static Connection conn = DBManager.getConnection();
  private static Admin admin;

  public static void addToBirthListFromMySQL() throws SQLException {



    try{
      Statement  stmt = conn.createStatement();



     ResultSet rs= stmt.executeQuery("SELECT * FROM birthtable");

       Birth list1;

        while (rs.next()) {
            String s1 = rs.getString(2);
            if (rs.wasNull()) {
                s1 = null;
            }
            String s2 = rs.getString(3);
            if (rs.wasNull()) {
                s2 = null;
            }
            String s3 = rs.getString(4);
            if (rs.wasNull()) {
                s3 = null;
            }
            String s4 = rs.getString(5);
            if (rs.wasNull()) {
                s4 = null;
            }
            String s5 = rs.getString(6);
            if (rs.wasNull()) {
                s5 = null;
            }
            String s6 = rs.getString(7);
            if (rs.wasNull()) {
                s6 = null;
            }


          list1 = new Birth(s1, s2, s3, s4, s5, s6);
          admin.birthList.add(list1);


        }




    }
    catch(SQLException e){





    }

}

My frame:

public class BirthList extends javax.swing.JFrame {

    private Admin admin;

    /** Creates new form BirthList */
    public BirthList(Admin admin) {
        initComponents();
        this.admin = admin;
        try {
            Manager.addToBirthListFromMySQL();
        } catch (SQLException ex) {
            Logger.getLogger(BirthList.class.getName()).log(Level.SEVERE, null, ex);
        }
        fillTable();
    }


public void fillTable() {

        String[] columNames = {"name", "family", "father name", "mother name", "date of birth", "place of birth"};
        List<Birth> birth = admin.getBirthList();
        Object[][] data = new Object[birth.size()][columNames.length];
        for (int i = 0; i < data.length; i++) {
            Birth birth1 = birth.get(i);
            data[i][0] = birth1.getName();
            data[i][1] = birth1.getFamily();
            data[i][2] = birth1.getFatherName();
            data[i][3] = birth1.getMotherName();
            data[i][4] = birth1.getDateOfBirth();
            data[i][5] = birth1.getPlaceOfBirth();


        }
        DefaultTableModel model = new DefaultTableModel(data, columNames);
        jTable1.setModel(model);
    }

    public boolean isCellEditable(int row, int col) {
        return true;
    }
}

StackTrace: "AWT-EventQueue-0" java.lang.NullPointerException        .Manager.addToBirthListFromMySQL(Manager.java:272)        AdminGUI.BirthList. (BirthList.java:35)        AdminGUI.BirthFrame.newButton1ActionPerformed (BirthFrame.java:127)        AdminGUI.BirthFrame.access $000 (BirthFrame.java:21)        AdminGUI.BirthFrame $1.actionPerformed(BirthFrame.java:58)        javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)        javax.swing.AbstractButton $Handler.actionPerformed(AbstractButton.java:2318)        javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)        javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)        javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)        java.awt.Component.processMouseEvent(Component.java:6038)        javax.swing.JComponent.processMouseEvent(JComponent.java:3265)        java.awt.Component.processEvent(Component.java:5803)        java.awt.Container.processEvent(Container.java:2058)        java.awt.Component.dispatchEventImpl(Component.java:4410)        java.awt.Container.dispatchEventImpl(Container.java:2116)        java.awt.Component.dispatchEvent(Component.java:4240)       at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322)       at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3986)       at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)        java.awt.Container.dispatchEventImpl(Container.java:2102)        java.awt.Window.dispatchEventImpl(Window.java:2429)        java.awt.Component.dispatchEvent(Component.java:4240)        java.awt.EventQueue.dispatchEvent(EventQueue.java:599)        java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)        java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)        java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)        java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)        java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)        java.awt.EventDispatchThread.run(EventDispatchThread.java:121)

272: admin.birthList.add(list1);

** , :

: javadebug .

* admin system.out.println(admin), :

classes.Admin@20be79 *

+1
4

, , , , NPE, , OP .

, () Object, , null.

SomeObject someObject1 = new SomeObject(); // References something.
SomeObject someObject2 = null; // References nothing.

, (null), , , NullPointerException, , null .

someObject1.doSomething(); // Works fine.
someObject2.doSomething(); // Throws NullPointerException.

. : , .

if (someObject2 == null) {
    someObject2 = new SomeObject();
}
someObject2.doSomething(); // No NPE anymore!


if (someObject2 != null) {
    someObject2.doSomething(); // No NPE anymore!
}

NPE stacktrace , . " 272 admin.birthList.add(list1);". , / ( dot .). admin.birthList, - birthList.add(list1). , , NPE. , admin null. , birthList null. , .

: ( ), . " " System.out.println() , / . , NPE. , ,

admin.birthList.add(list1);

, :

System.out.println("admin: " + admin);
List<Birth> birthList = admin.birthList;
System.out.println("birthList: " + birthList);
birthList.add(list1);

, - null. :

if (admin == null) throw new NullPointerException("admin is null!");
List<Birth> birthList = admin.birthList;
if (birthList == null) throw new NullPointerException("birthList is null!");
birthList.add(list1);

, , , null.

List<Birth> birthList = admin.birthList; // If NPE line points here, then admin is null.
birthList.add(list1); // If NPE line points here, then birthList is null.
+3

, , Admin null, NPE addToBirthListFromMySQL()

public BirthList(Admin admin) {
        initComponents(); // where do you set this.admin to the parameter 'admin' ?

Admin Manager

public BirthList(Admin admin) {
        this.admin = admin
        Manager.admin = admin
        initComponents();

( : , )

, :

debug: Have no FileObject for C:\Program Files\Java\jdk1.6.0_02\jre\lib\sunrsasign.jar

Have no FileObject for C:\Program Files\Java\jdk1.6.0_02\jre\classes**

, 1.6 1.5 runtime / .

:

:

  • . (, )
  • ...
    . set path="D:\...\JDK1.5\bin"
    . set classpath="D:\...\JDK1.5\bin"
    . set java_home="D:\...\JDK1.5"
  • . (Project Properties->Libraries).
+2

, , , , - "private static Admin admin"; ?

0

272 Manager.java:

admin.birthList.add(list1);

admin null, , : birthlist - null, , add() .

, admin :

public class Admin {
    public List<Birth> birthList; //the visibility seems to be public
    ...
}

and you never initialize a class attribute birthlist. Therefore, either initialize it inline, or in the constructor, and in the method init(), etc., but do it somewhere. For example, inline:

public class Admin {
    public List<Birth> birthList = new ArrayList<Birth>(); 
    ...
}

Actually, I'm not sure how you instantiate a adminstatic instance of your class Manager, but this is another story.

0
source

Source: https://habr.com/ru/post/1727628/

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