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Thread: need help with my java program

  1. #1
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    Default need help with my java program

    I'm writing a program to calculate the final yield of a person investing a initial amount of money over a set amount of time with a set interest rate. I get the following error when compiling the code:

    Exception in thread "main" java.lang.NullPointerException
    at java.awt.Container.addImpl(Unknown Source)
    at java.awt.Container.add(Unknown Source)
    at calculator.<init>(calculator.java:62)
    at calculator.main(calculator.java:92)

    Here is the code for my java program:

    import javax.swing.*;
    import java.awt.*;
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
     
    public class calculator extends JFrame{
    	private JButton calcButton, clearButton;
    	private JLabel originalDeposit, interestRate, timeInvested;
    	private JLabel resultDisplay;
    	private JTextField originalField, interestField, timeField;
    	private JPanel panel1, panel2, panel3,panel4,panel5;
    	double deposit,interest,time,newBalance;
     
    	public calculator(){
    		super("App to calculate the yield of an invesment");
    		setSize(400,400);
    		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    		setLayout(new GridLayout(6,1));
    		originalDeposit = new JLabel("Enter amount of original deposit");
    		originalField = new JTextField(7);
    		interestRate = new JLabel("Enter the annual interest rate");
    		interestField = new JTextField(5);
    		timeInvested = new JLabel("Enter the years of invesment as a whole number");
    		calcButton = new JButton("Calculate");
    		clearButton = new JButton("Clear");
    		resultDisplay = new JLabel("The new balance in the investment account will be" + newBalance);
     
    		calcButton.addActionListener(new ActionListener(){
    			public void actionPerformed(ActionEvent e){
     
    			String caption = e.getActionCommand();
    			if(e.getSource() instanceof JButton){
    				Object String;
    				if("Calculate".equals(caption))
    					getNewBalance();
    				resultDisplay.setText("The new balance in the investment account will be" + newBalance);
    				}
    			}
    		});
     
    		clearButton.addActionListener(new ActionListener(){
            	public void actionPerformed(ActionEvent e){
     
    			String caption = e.getActionCommand();
    			if(e.getSource() instanceof JButton){
    				if("Clear".equals(caption))
    					clearFields();
    				}
            	}
            });
     
     
     
    		panel1 = new JPanel();
    		panel1.add(originalDeposit);
    		panel1.add(originalField);
    		panel2 = new JPanel();
    		panel2.add(interestRate);
    		panel2.add(interestField);
    		panel3 = new JPanel();
    		panel3.add(timeInvested);
    		panel3.add(timeField);
    		panel4 = new JPanel();
    		panel4.add(calcButton);
    		panel4.add(clearButton);
    		panel5 = new JPanel();
    		panel5.add(resultDisplay);
    		add(panel1);
    		add(panel2);
    		add(panel3);
    		add(panel4);
    		add(panel5);
    	}
     
    	public double getNewBalance(){
    		deposit = Double.parseDouble(originalField.getText().trim());
    		interest = Double.parseDouble(interestField.getText().trim());
    		time = Double.parseDouble(timeField.getText().trim());
     
    		newBalance = deposit*(1+(interest/1));
     
    		return newBalance;
    	}
     
    	public void clearFields(){
    		originalField.setText(" ");
    		interestField.setText(" ");
    		timeField.setText(" ");
    	}
     
    	public static void main(String args[]){
    		calculator cal = new calculator();
    	}
    }


  2. #2
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    Default Re: need help with my java program

    Something is being added to your user interface that is null. Make sure all your variables are initialized (hint: where is timeField constructed?)

  3. #3
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    Default Re: need help with my java program

    I initialized the variables the following way:

    	private JButton calcButton, clearButton;
    	private JLabel originalDeposit, interestRate, timeInvested;
    	private JLabel resultDisplay;
    	private JTextField originalField, interestField, timeField;
    	private JPanel panel1, panel2, panel3,panel4,panel5;
    	double deposit=0.0,interest=0.0,time=0.0,newBalance=0.0;

    compared to how it was before:

    private JButton calcButton, clearButton;
    	private JLabel originalDeposit, interestRate, timeInvested;
    	private JLabel resultDisplay;
    	private JTextField originalField, interestField, timeField;
    	private JPanel panel1, panel2, panel3,panel4,panel5;
    	double deposit,interest,time,newBalance;

    I still get the following error message:


    Exception in thread "main" java.lang.NullPointerException
    at java.awt.Container.addImpl(Unknown Source)
    at java.awt.Container.add(Unknown Source)
    at calculator.<init>(calculator.java:62)
    at calculator.main(calculator.java:92)

  4. #4
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    Default Re: need help with my java program

    Quote Originally Posted by omegared33 View Post
    I initialized the variables the following way:

    private JButton calcButton, clearButton;
    	private JLabel originalDeposit, interestRate, timeInvested;
    	private JLabel resultDisplay;
    	private JTextField originalField, interestField, timeField;
    	private JPanel panel1, panel2, panel3,panel4,panel5;
    	double deposit,interest,time,newBalance;

    I still get the following error message:


    Exception in thread "main" java.lang.NullPointerException
    at java.awt.Container.addImpl(Unknown Source)
    at java.awt.Container.add(Unknown Source)
    at calculator.<init>(calculator.java:62)
    at calculator.main(calculator.java:92)
    the error tells you where you have not initialized the variable Line 62 see below
    timeField = new JTextField();

  5. #5
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    Default Re: need help with my java program

    don't forget to

    public static void main(String args[]){
    		calculator cal = new calculator();
            cal.setVisible(true);
    	}

  6. #6
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    Default Re: need help with my java program

    I implemented the change in the main method; however I'm not sure how you are asking for line 62 to be edited.

    the original syntax is:

    panel3.add(timeField);

  7. #7
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    Default Re: need help with my java program

    Quote Originally Posted by omegared33 View Post
    I implemented the change in the main method; however I'm not sure how you are asking for line 62 to be edited.

    the original syntax is:

    panel3.add(timeField);
    exactly, timefield is a variable needs to be initialized
     timeField = new JTextField()
    some where. Its not your trying to use a null JTextField

  8. #8
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    Default Re: need help with my java program

    Quote Originally Posted by omegared33 View Post
    I initialized the variables the following way:

    	private JButton calcButton, clearButton;
    	private JLabel originalDeposit, interestRate, timeInvested;
    	private JLabel resultDisplay;
    	private JTextField originalField, interestField, timeField;
    	private JPanel panel1, panel2, panel3,panel4,panel5;
    	double deposit=0.0,interest=0.0,time=0.0,newBalance=0.0;
    Perhaps you initialized your double variables, but what about your object variables? They must be instantiated prior to use (for example "myTextField = new JTextField()" ), and while many have been there is at least one that has not been.

  9. #9
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    Default Re: need help with my java program

    all i did was add this in your code and ran it
    //your code
                    originalDeposit = new JLabel("Enter amount of original deposit");
    		originalField = new JTextField(7);// <----- here you did
    		interestRate = new JLabel("Enter the annual interest rate");
    		interestField = new JTextField(5); //<---- here you did
    		timeInvested = new JLabel("Enter the years of invesment as a whole number");
    		calcButton = new JButton("Calculate");
    		clearButton = new JButton("Clear");
    		resultDisplay = new JLabel("The new balance in the investment account will be" + newBalance);
     
            //added textField variable initialized
            timeField = new JTextField(10);  //<--- you missed this guy

    works fine for me.

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