Low level version of drawing interface (explain each step in detail)

package com.lk.login1029;

import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;



// Don't look at the source documents and references in the whole process, plus some of your own ideas 
// First create a form 
// The size of the form needs to be set ; In the middle ; When the form closes, the program closes itself and ends ;
// You need to add buttons to the form ; Note that the button can only be added when the form is displayed ; Brushes and the like ;
// When the demand reaches the button to be added, you will think about where to add it , So you need to add a layout manager 
// When you need to add multiple buttons, you find that their steps are similar ; So use functions instead of repetitive work 
// Need to add text ; The button is created by itself ; Form required ; Need a listener 
// You need to install a listener on the form ; By looking at the original code, it is found that the contents in brackets need an interface data type ; When you need interface data types, you need to rewrite a class as data 
// You need an array to match str Fill the occupied position 
// When you need to add color buttons, you find ; The contents of the array have changed ; So create a function to add a button with all colors 



public class DrawUI2 {
	String[] strs = {" A straight line "," Square "," The ellipse "," an isosceles triangle "," Any triangle "," Freeform "};// Note that it is stored in array form, not in list form 
	Color[] color = {Color.black,Color.blue,Color.red,Color.green,Color.yellow};// Color is also a type 
 public void showUI() {
	JFrame jf =new JFrame();
	jf.setSize(900, 900);
	jf.setLocationRelativeTo(null);
	jf.setDefaultCloseOperation(3);
	jf.setVisible(true);
	FlowLayout flow =new FlowLayout();
	jf.setLayout(flow);
	
	//JButton jb =new JButton("text");
	//jf.add(jb);
	//jb.addActionListener(mouse);
	Mouse2 mou =new Mouse2();
	// Add listeners to the interface 
	jf.addMouseListener(mou);
	// Add multiple buttons on the interface 
	// This kind of general belt xxx. Is either an attribute or a method 
	for (int i=0;i<strs.length;i++) {
		AddButton(strs[i],jf,mou);}
	for (int i=0;i<color.length;i++) {
		AddColor(color[i],jf,mou);
	}
	 Graphics gr = jf.getGraphics();
	 mou.g = gr;
	
 }
 public void AddButton(String str,JFrame jf,ActionListener al) {
	 JButton jb = new JButton(str);
	 jf.add(jb);
	 jb.addActionListener(al);
	 
}
 public void AddColor(Color color,JFrame jf,ActionListener al) {
	 JButton jb = new JButton(" ");// The space function increases the size of the button 
	 jb.setBackground(color);
	 jf.add(jb);
	 jb.addActionListener(al);
 }
 public static void main(String[] args) {
	 DrawUI2 ui=new DrawUI2();
	 ui.showUI();
	 }
 }

package com.lk.login1029;
import javax.swing.*;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

import javax.swing.JButton;

public class Mouse2 implements ActionListener,MouseListener{
	Graphics g;
	String typestr,str ;
	int x1,y1,x2,y2;

	@Override
	public void actionPerformed(ActionEvent e) {
		// TODO Auto-generated method stub
		System.out.println(" The button is clicked ");
		 str =e.getActionCommand();
		if(str.equals(" ")){
			System.out.println(" This is a color button ");
			JButton jbu =(JButton)e.getSource();// This means to record the event source obtained 
			Color color = jbu.getBackground();
			g.setColor(color);// The brush gets the background color 
			
		}
		else {
			typestr =str;
		}
		
		
	}

	@Override
	public void mouseClicked(MouseEvent e) {
		// TODO Auto-generated method stub
		System.out.println(" The button is clicked ");
		
	}

	@Override
	public void mousePressed(MouseEvent e) {
		// TODO Auto-generated method stub
		x1 = e.getX();
		y1 =e.getY();
	}

	@Override
	public void mouseReleased(MouseEvent e) {
		// TODO Auto-generated method stub
		x2 =e.getX();
		y2 = e.getY();
		g.drawLine(x1, y1, x2, y2);
	}

	@Override
	public void mouseEntered(MouseEvent e) {
		// TODO Auto-generated method stub
		System.out.println(" Get into ");
		
	}

	@Override
	public void mouseExited(MouseEvent e) {
		// TODO Auto-generated method stub
		System.out.println(" sign out ");
	}
	
}

The front is the whole program

// First Create a form
// Form needs Set size Ah, something like that ; In the middle ; When When the form closes, the program closes itself and ends ;
// You need to add buttons to the form ; Note that the button can only be added when the form is displayed ; Brushes and the like ;
// When the demand reaches the button to be added, you will think about where to add it , So you need to add Layout manager
// When you need to add multiple buttons, you find that their steps are similar ; So use functions instead of repetitive work
// Need to add text ; The button is created by itself ; Form required ; Need a listener
// You need to install a listener on the form ; By looking at the original code, it is found that the contents in brackets need an interface data type ; When interface data types are required Rewrite a class as data
// You need an array to match str Fill the occupied position
// When you need to add color buttons, you find ; The contents of the array have changed ; So create a Function to add a button with all colors