Question

我不知道我错过了哪个概念，我编写了一个小项目，它使用java arraylist和GUI维护联系人。应用程序中有添加，删除，搜索，第一个，最后一个，上一个，下一个，退出，清除按钮。所有按钮除了第一个和最后一切都正常工作。我得到的问题是在函数Displayfirst **（）

中

这是代码

AddressBookDemo.java

pywhois

PersonDAO.Java

    public void actionPerformed (ActionEvent e){

        if (e.getSource () == jbbSave){
             savePerson();
             clear(); 
        }

        else if (e.getSource() == jbnDelete){
             deletePerson();
             clear();
        }

        else if (e.getSource() == jbnFirst){
             displayFirstRecord();

                    clear(); 
        }

        else if (e.getSource() == jbnLast){
             displayLastRecord();
             clear(); 
        }

        else if (e.getSource() == jbnSearch){
             searchPerson();
        } 

        else if (e.getSource() == jbnForward){
             displayNextRecord(); 
        }

        else if (e.getSource() == jbnBack){
            displayPreviousRecord();
        }

        else if (e.getSource() == jbnClear){
            clear();
        }

        else if (e.getSource() == jbnExit){         
            System.exit(0);
        }

    }
      public void searchPerson() {

        name = jtfName.getText();
        name = name.toUpperCase();
        /*clear contents of arraylist if there are any from previous search*/
        personsList.clear();



        if(name.equals("")){
            JOptionPane.showMessageDialog(null,"Please enter person name to search.");
        }
        else{
            /*get an array list of searched persons using PersonDAO*/
            personsList = pDAO.searchPerson(name);

            if(personsList.size() == 0){
                JOptionPane.showMessageDialog(null, "No records found.");
                //Perform a clear if no records are found.
                clear();
            }
            else
            {
                /*downcast the object from array list to PersonInfo*/
                PersonInfo person = (PersonInfo) personsList.get(0);

                 // displaying search record in text fields 
                jtfName.setText(person.getName());
                jtfAddress.setText(person.getAddress());
                jtfPhone.setText(""+person.getPhone());
                jtfEmail.setText(person.getEmail());
            }
        }

     }
****
public void displayFirstRecord(){

         // dec in recordNumber to display previous person info, already 
         //stored in personsList during search                  


        if(pDAO.getpersonsList().size() == 0 ){
            JOptionPane.showMessageDialog(null, "There are no records"); 

            /*if user has reached the begining of results, disable back button*/
            jbnForward.setEnabled(true);
            jbnBack.setEnabled(false);

             // inc by one to counter last dec

        }else{

                        System.out.println(pDAO.getpersonsList().size());
       personsList = pDAO.getpersonsList();
     PersonInfo person=(PersonInfo)personsList.get(0);
            // displaying search record in text fields 
            jtfName.setText(person.getName());
            jtfAddress.setText(person.getAddress());
            jtfPhone.setText(""+person.getPhone());
            jtfEmail.setText(person.getEmail());
                        //jbnFirst.setEnabled(false);
        }

     }

public void displayLastRecord(){

         // dec in recordNumber to display previous person info, already 
         //stored in personsList during search                  


        if(pDAO.getpersonsList().size()== 0 ){
            JOptionPane.showMessageDialog(null, "There are no records"); 

            /*if user has reached the begining of results, disable back button*/
            jbnForward.setEnabled(true);
            jbnBack.setEnabled(false);

             // inc by one to counter last dec
                    }else{
            jbnForward.setEnabled(true);
            PersonInfo person = (PersonInfo) pDAO.getpersonsList().get(pDAO.getpersonsList().size()-1);

            // displaying search record in text fields 
            jtfName.setText(person.getName());
            jtfAddress.setText(person.getAddress());
            jtfPhone.setText(""+person.getPhone());
            jtfEmail.setText(person.getEmail());
        }

     }

********************

PersonInfo.Java

public class PersonDAO{      


    private ArrayList<PersonInfo> personsList;

*******************************


    public ArrayList searchPerson(String name)
    {
            ArrayList<PersonInfo> personsList1=new ArrayList<>();

            for (PersonInfo personsList2 : personsList) {
                PersonInfo p = (PersonInfo) personsList2;
                if(p.getName() == null ? name == null : p.getName().equals(name)){
                    personsList1.add(p);
                    break;
                }
            }
         return personsList1;
            }

Answer 1

您正在调用assertRedirects方法，该方法会清除clear()的文字

JLable

...

else if (e.getSource() == jbnFirst){
    displayFirstRecord();
    clear(); 
}
else if (e.getSource() == jbnLast){
    displayLastRecord();
    clear(); 
}

.... public void displayFirstRecord(){ .... jtfName.setText(person.getName()); jtfAddress.setText(person.getAddress()); jtfPhone.setText(""+person.getPhone()); jtfEmail.setText(person.getEmail()); .... }方法大致相同。

displayLastRecord()

Arraylist没有返回对象

1 个答案: