this is the code used to make the calculator work, I have not fully finished it yet. I'm am new to Java programming (at beginners level).

//listen to action from the buttons
import java.awt.event.ActionListener;
 
//implement event for button
import java.awt.event.ActionEvent;
 
import javax.swing.JButton;
 
public class CalcFunction  implements ActionListener{
 
/*reference to calculator using parent so the events for the button coded*/
	Calculator parent;
 
	//used to store the math function
	char Selection=' ';
 
	//current result stored in the calculator is 0.
	double Current=0;
 
 
 
	//CalcFunction stores the reference to the to the Calculator class.
	CalcFunction(Calculator parent){
	this.parent = parent;
	}
 
@Override //implement the event for the buttons and the text field
public void actionPerformed(ActionEvent e) {
 
/*a gets the source of the button that was clicked in the calculator. Basically any button
 * that was clicked, the ActionListener will check which button is clicked and it will store
 * the clicked button's value. This will be stored in the new button created called
 *  clickedButton*/
	JButton clickedButton = (JButton) e.getSource();
 
	/*the texts that are displayed in the calculator text field will be stored in the variable
	 * named textfieldDisplay.*/
	String textfieldDisplayed = parent.inPutText.getText();
 
	//the value of the answers displayed will be displayed as 0.0 (in a a decimal value).
	double displayValue=0;
 
	if (!"".equals(textfieldDisplayed)){
		//
		displayValue= Double.parseDouble(textfieldDisplayed);
		Object src = e.getSource();
 
 
		if (src == parent.btnPlus){
			Selection = '+'; 
			Current=displayValue;
			parent.inPutText.setText("");
 
			}
			else if (src == parent.btnMinus){
			Selection = '-'; 
			Current=displayValue;
			parent.inPutText.setText("");
			}
 
			else if (src == parent.btnDivide){
			Selection = '/'; 
			Current=displayValue; 
			parent.inPutText.setText("");
			} 
 
			else if (src == parent.btnMultiply){
			Selection = '*';
			Current=displayValue;
			parent.inPutText.setText("");
			} 
 
	if(Selection == '+'){
		Selection='+';
		Current+=displayValue;
		parent.inPutText.setText(""+ Current);
	//end bracket for parent.btnPlus	
	}
	else if(Selection == '-'){
		Selection='-';
		Current-=displayValue;
		parent.inPutText.setText(""+ Current);
 
 
		//end bracket for parent.btnMinus	
	}
	else if(Selection == '*'){
		Selection='*';
		Current*=displayValue;
		parent.inPutText.setText(""+ Current);
 
 
		//end bracket for parent.btnMultiply	
	}
 
	else if(Selection == '/'){
		Selection='/';
 
		Current/=displayValue;
 
		parent.inPutText.setText("" + Current);
 
 
		//end bracket for parent.btnDivide	
	}
	else{
		// For all numeric buttons append the button's
		// label to the text field
		String ButtonLabel= clickedButton.getText();
		parent.inPutText.setText(textfieldDisplayed + ButtonLabel);
 
		//end bracket for else.
		}
 
 
 
 
	}
 
 
//end bracket for actionPerformed	
}
 
}


below is the code used to set the calculator (how it looks like):
import java.awt.*;
//
import javax.swing.*;
 
 
 
public class Calculator{
 
 
	//sets the frame which is the window of the calculator. Where the buttons and the contents are
	//presented. Basically its the background box. This frame is assigned the name "Calculator".
	JFrame Frame = new JFrame("Calculator");	
 
	//sets the text box for the calculator. the maximum field size is 30.
	JTextField inPutText = new JTextField(30);
 
	//this JPanel is created to separately to add the buttons uniquely on its on section.
	//its almost like a graphical variable to store the buttons.
	JPanel buttonPanel = new JPanel();
	//number buttons
	JButton btn1 = new JButton("1");
	JButton btn2 = new JButton("2");
	JButton btn3 = new JButton("3");
	JButton btn4 = new JButton("4");
	JButton btn5 = new JButton("5");
	JButton btn6 = new JButton("6");
	JButton btn7 = new JButton("7");
	JButton btn8 = new JButton("8");
	JButton btn9 = new JButton("9");
	JButton btn0 = new JButton("0");
 
	//math buttons
	JButton btnPlus = new JButton("+");
	JButton btnMinus = new JButton("-");
	JButton btnMultiply = new JButton("*");
	JButton btnDivide = new JButton("/");
 
	//full stop and equal button.
	JButton btnEqual = new JButton("=");
	JButton btnBulletPoint = new JButton(".");
 
 
	public Calculator(){
		//sets a grid layout for the calculator 4 by 1.
		GridLayout buttonBorder = new GridLayout(4,1);
 
		//sets the frame visible to view the calculator itself.
		Frame.setVisible(true);
 
		//sets the frame size by 200 by 200.
		Frame.setSize(200,200);
		//sets the button panel visible to view the buttons.
		buttonPanel.setVisible(true);
 
		//the button panel is assigned with grid layout.
		buttonPanel.setLayout(buttonBorder);
 
		//added the buttons onto the Frame (Window)
		 Frame.add(buttonPanel);
 
		//assigning the buttons to the Frame using the panel made for the buttons.
		buttonPanel.add(btn1);
		buttonPanel.add(btn2);
		buttonPanel.add(btn3);
		buttonPanel.add(btnPlus);
		buttonPanel.add(btn4);
		buttonPanel.add(btn5);
		buttonPanel.add(btn6);
		buttonPanel.add(btnMinus);
		buttonPanel.add(btn7);
		buttonPanel.add(btn8);
		buttonPanel.add(btn9);
		buttonPanel.add(btnMultiply);
		buttonPanel.add(btn0);
		buttonPanel.add(btn0);
		buttonPanel.add(btnBulletPoint);
		buttonPanel.add(btnEqual);
		buttonPanel.add(btnDivide);
 
 
		//assigning the text box on the Frame itself at the top of the box.
		Frame.add(inPutText,BorderLayout.NORTH);
 
		CalcFunction function= new CalcFunction(this);
		btn1.addActionListener(function);
		btn2.addActionListener(function);
		btn3.addActionListener(function);
		btn4.addActionListener(function);
		btn5.addActionListener(function);
		btn6.addActionListener(function);
		btn7.addActionListener(function);
		btn8.addActionListener(function);
		btn9.addActionListener(function);
		btn0.addActionListener(function);
		//public Calculator end bracket	
 
 
 
 
	}
		public static void main(String[] args)
		{
			//
			Calculator calc = new Calculator();
 
 
	//end of main 
		}
	//end of class Calculator.	
 
 
	}