JTextField.setText（）不能在方法中作为数组使用

Question

new Java programmer here so I might have a basic question here. I am making an array of JTextFields. I want to use setText outside of the class in a public method but it does not work. However, I am able to use setText in the class (not in a method). I am not sure why. Here is some code as a SSCCE to show what I am experiencing. import java.awt.BorderLayout; import javax.swing.*;

public class testSetText extends JFrame 
{
    private JPanel          panel;
    private JTextField[]    arrayField;
    private JTextField      singleField;

    public testSetText()
    {
        // Specify an action for close button
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // Make a panel
        panel = new JPanel();

        // Make array of JTextField components
        JTextField[] arrayField = new JTextField[2];
        for (int i = 0; i < 2; i++)
        {
            arrayField[i] = new JTextField(10);
            arrayField[i].setEditable(false);
            arrayField[i].setText("<>!");
            panel.add(arrayField[i]);
        }

        // Make just one JTextField component
        singleField = new JTextField(10);
        singleField.setText("Works here");
        panel.add(singleField);

        // Add to panel to frame
        add(panel);

        // Pack the contents of the window and display it
        pack();
        setVisible(true);

        // This will work!
        arrayField[0].setText("Array index in class");

        // This won't? Why?
        setInMethodWithArray();

        // Is this a problem with JTextField itself? Let me try a single element
        setInMethodWithSingleElement(); 

        // Hmmm so an element in an array of JTextFields can be addressed with setText in a class but not 
        // in a method in same class with same statement. But a single JTextField can be used in a method
        // by that same class. Why do arrays behave so differently?

        // EDIT: So I misunderstood, it does not work with a non array as well either!!
    }

    public void setInMethodWithArray()
    {
        arrayField[1].setText("This text will never show up");
    }

    public void setInMethodWithSingleElement()
    {
        //singleField.setText("Works here as non-array"); <--- before edit
        singleField.setText("nevermind, it does not work here either");
    }

    public static void main(String[] args)
    {
        new testSetText();
    }
}

Answer 1

you should declare arrayField[] in class area so array Field is accessible from setInMethodWithArray() method.

JTextField[] arrayField = new JTextField[2]; //class area

in constructor initial it

 arrayField[i]= new JTextField(10);
 arrayField[i].setEditable(false);

---

yes this is work

 arrayField[0].setText("Array index in class"); 

because arrayField in the constructor scope ..and you are accessing arrayField Within constructor .so it works..

This won't? Why?

 setInMethodWithArray(); 

because method setInMethodWithArray() can't access arrayField[] because it's not in method scope or in class scope.that's because you have declare it in the constructor so after constructor code block execute arrayField doesn't exist .it's reference lost because it's local variable ..

 public void setInMethodWithArray() { arrayField[1].setText("This text will never show up"); } 

now set can access arratField[] so now your code will work

 import java.awt.BorderLayout; import javax.swing.*; public class testSetText extends JFrame { private JPanel panel; private JTextField singleField; // Make array of JTextField components private JTextField[] arrayField = new JTextField[2]; public testSetText() { // Specify an action for close button setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // Make a panel panel = new JPanel(); for (int i = 0; i < 2; i++) { arrayField[i] = new JTextField(10); arrayField[i].setEditable(false); arrayField[i].setText("<>!"); panel.add(arrayField[i]); } // Make just one JTextField component singleField = new JTextField(10); singleField.setText("Works here"); panel.add(singleField); // Add to panel to frame add(panel); // Pack the contents of the window and display it pack(); setVisible(true); // This will work! arrayField[0].setText("Array index in class"); // This won't? Why? setInMethodWithArray(); // Is this a problem with JTextField itself? Let me try a single element setInMethodWithArray(); // Hmmm so an element in an array of JTextFields can be addressed with setText in a class but not // in a method in same class with same statement. But a single JTextField can be used in a method // by that same class. Why do arrays behave so differently? } public void setInMethodWithArray() { arrayField[1].setText("This text will never show up"); } public void setInMethodWithSingleElement() { singleField.setText("Works here as non-array"); } public static void main(String[] args) { new testSetText(); } } 

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