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Thread: java.lang.NullPointerExpectation:null (in java.awt.Container) when adding a JPanel

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    Post java.lang.NullPointerExpectation:null (in java.awt.Container) when adding a JPanel

    Hi i am having an issue with this error "java.lang.NullPointerExpectation:null (in java.awt.Container)", it wasn't happening until i added the jpanel any solutions?

    package folderCreating;
    import java.io.*;
    import javax.swing.*;
    import java.awt.*;
    import java.awt.event.*;
     
     
    public class window extends JFrame{
     
        private JTextField textField1;
        private JButton button1;
        private JTextField textField2;
        private JButton button2;
        private JButton button3;
        private JButton button4;
        public static String fileInput;
        public static String folderInput;
     
        public window(){
     
            super("File and Folder Manager");  
     
            setLayout(new FlowLayout());
     
            JPanel p1 = new JPanel();
     
            p1.add(textField1);
            p1.add(button2);
            add(p1);
     
            textField2 = new JTextField(20);
            add(textField2);
     
            button1 = new JButton("Create Folder");
            add(button1);
     
            textField1 = new JTextField(20);
            add(textField1);
     
            button2 = new JButton("Create File");
            add(button2);
    }


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    Default Re: java.lang.NullPointerExpectation:null (in java.awt.Container) when adding a JPane

    which line produces the error?

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    Default Re: java.lang.NullPointerExpectation:null (in java.awt.Container) when adding a JPane

    Step through the code as the computer would. First call the constructor:
    public window(){
    so far so good. continue...
    setLayout(new FlowLayout());
    JPanel p1 = new JPanel();
    ok.... go on.......
    p1.add(textField1);
    Stop. textField1 has not been initialized. (can not add 'null' to a JPanel)
    textField1 must have been assigned a value first. This is not the only variable with the problem.

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    Default Re: java.lang.NullPointerExpectation:null (in java.awt.Container) when adding a JPane

    well according to your code the compiler is right, you have not initialized the variable textField1,
    you need to create a new object with the new keyword, and then you can add it.
    edit : the order of which is important, first make object, then add it.

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