[英]creating objects in java - stackoverflow error
假設我有兩個班級A和B。 如果我在B類創建類A的對象,也可以創建在A類B類的對象時,它會導致堆棧溢出錯誤。 一個解決這個問題是,我可以在B類,並且反之亦然創建的任何函數內部類A的對象,但如果我這樣做,那么類A的對象創建的每個時間在其中創建類A的對象,特定功能,叫做。
問題是我如何才能使A類和B類對象彼此有效地相互融合?
考慮下面的例子。
房間等級
public class Room {
String roomno;
String reserved;
String category;
String airconditioned;
String bedtype;
String rent;
Connection con;
PreparedStatement ps;
ResultSet rs;
AddRoom adr = new AddRoom();
RemoveRoom rr = new RemoveRoom();
UpdateRoom ur = new UpdateRoom();
// AllRooms alr = new AllRooms();
public Room()
{
roomno = "";
reserved = "";
category = "";
airconditioned = "";
bedtype = "";
rent = "";
make_connection();
}
public void make_connection()
{
try{
String driver = "net.ucanaccess.jdbc.UcanaccessDriver";
Class.forName(driver);
String login = "jdbc:ucanaccess://C:\\MsDatabase\\EmployeeDB.accdb";
con = DriverManager.getConnection(login);
}catch(Exception ex){ System.out.println(ex);}
}
public void add_room(AddRoom obj)
{
try{
adr = obj;
if("".equals(adr.get_jtextfield1().getText())||"".equals(adr.get_jtextfield2().getText())||
"".equals(adr.get_jtextfield3().getText())||"".equals(adr.get_jtextfield4().getText())||
"".equals(adr.get_jtextfield5().getText())||"".equals(adr.get_jtextfield6().getText()))
{
JOptionPane.showMessageDialog(null, "None of the fields can be left empty");
}
else
{
roomno = adr.get_jtextfield1().getText();
reserved = adr.get_jtextfield2().getText();
category = adr.get_jtextfield3().getText();
airconditioned = adr.get_jtextfield4().getText();
bedtype = adr.get_jtextfield5().getText();
rent = adr.get_jtextfield6().getText();
String sql = "INSERT INTO RoomInfo(RoomNumber,Reserved,RoomCategory,AirConditioned,BedType,RentPerDay)"
+ "VALUES(?,?,?,?,?,?)";
ps = con.prepareStatement(sql);
ps.setInt(1, new Integer(roomno));
ps.setString(2, reserved);
ps.setString(3, category);
ps.setString(4, airconditioned);
ps.setString(5, bedtype);
ps.setInt(6, new Integer(rent));
ps.executeUpdate();
JOptionPane.showMessageDialog(null, "Room Added Successfully");
}
}catch(Exception ex){
JOptionPane.showMessageDialog(null, "Input in Room Number and "
+ "Rent Per Day should be a number");
}
}
}
AddRoom類
public class AddRoom extends javax.swing.JFrame {
Room objr = new Room();
public AddRoom() {
initComponents();
}
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
//Room objr = new Room();
objr.add_room(this);
}
private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {
AdminHome admh = new AdminHome();
admh.setVisible(true);
dispose();
}
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
new AddRoom().setVisible(true);
}
});
}
public JTextField get_jtextfield1()
{
return jTextField1;
}
public JTextField get_jtextfield2()
{
return jTextField2;
}
public JTextField get_jtextfield3()
{
return jTextField3;
}
public JTextField get_jtextfield4()
{
return jTextField4;
}
public JTextField get_jtextfield5()
{
return jTextField5;
}
public JTextField get_jtextfield6()
{
return jTextField6;
}
// Variables declaration - do not modify
private javax.swing.JButton jButton1;
private javax.swing.JButton jButton2;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
private javax.swing.JLabel jLabel3;
private javax.swing.JLabel jLabel4;
private javax.swing.JLabel jLabel5;
private javax.swing.JLabel jLabel6;
private javax.swing.JLabel jLabel7;
private javax.swing.JPanel jPanel1;
private javax.swing.JTextField jTextField1;
private javax.swing.JTextField jTextField2;
private javax.swing.JTextField jTextField3;
private javax.swing.JTextField jTextField4;
private javax.swing.JTextField jTextField5;
private javax.swing.JTextField jTextField6;
// End of variables declaration
}
請注意,我已經在AddRoom類中創建了Room類的對象,並且還在Room類中創建了AddRoom類的對象。 現在,如果執行此操作,則會出現堆棧溢出錯誤,但是如果我在AddRoom類的任何函數中將Room類的對象作為對象,則不會顯示堆棧溢出錯誤,並且程序可以正常運行。
您正在使用Circle參考/依賴性,這不是一個好主意...
您需要實現的是回調,因此A可以從B調用方法,並且B可以通知A參見上圖:
//Interface
public interface ICallback{
void onMessage(String msg);
}
//the class A call methods from B
public class A implements ICallback{
private B b;
public A(){
b= new B();
b.setCallback(this);
b.printSomething(5);
b.printSomething(0);
}
@Override
public void onMessage(String msg){
}
}
//the Class B can communicate to A with the callback
public class B {
private ICallback cb;
public B(){
}
public void setCallback(ICallback cb){
this.cb = cb;
}
public void printSomething(int i){
if(i==0){
cb.onMessage("this is zero");
}
}
}
如何有效地使A類和B類的對象相互內部?
不建議使用Java(或任何OOP語言)執行此操作,因為它會創建循環依賴項。
如果處理不當,將導致諸如StackOverflowError
異常,或者在程序/應用程序運行時會在解析依賴項以創建對象時發生異常(如果使用,則IOC容器(如Spring)將引發異常)。
因此,即使您在沒有上述問題的情況下進行管理, 在代碼內部的Java類或包之間創建循環依賴關系也不是一個好習慣,因為這將很難理解/維護,並且代碼復雜度很高 。 這就是為什么存在諸如FindBugs之類的代碼質量工具來幫助標識循環依賴項的原因,以便我們在開發過程中避免使用它們。
您可以在此處查看有關同一主題的更多詳細信息。
不確定100%的意思,您是否有類似的課程?...
public class A {
private B b;
public void setB(B b) {
this.b = b;
}
}
public class B {
private A a;
public void setA(A a) {
this.a = a;
}
}
您要創建一個帶有“ B”的“ A”嗎? 例如...
public class Factory {
public static A createA() {
A a = new A();
B b = new B();
a.setB(b);
b.setA(a);
return a;
}
}
這有幫助嗎?
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