Java Plot

In Java, Java Plot is a term which is mainly use for plotting coordinates on a cartesian plane. In Java, plotting of graph is done by using several topics of core Java. For plotting, we use swing, awt, and awt.geom.

We use Swing package to use Jlabel, JButtons, and JPanel in our program.
We use AWT (Abstract Window Toolkit) to make a graphical user interface for front-end of the project.
The awt.geom package is used to perform two-dimensional geometry operations.

In order to plot the point on a graph, we use several methods of graphics such as draw(), setPaint(), and Fill() etc. Let's take an example of a graph and understand how we can plot coordinates in Java.

PlotExample.java

//import require classes and packages
import java.awt.*;
import javax.swing.*;
import java.awt.geom.*;

//Extends JPanel class
public class PlotExample extends JPanel{
	//initialize coordinates
    int[] cord = {65, 20, 40, 80};
    int marg = 60;
    
    protected void paintComponent(Graphics grf){
    	//create instance of the Graphics to use its methods
        super.paintComponent(grf);
        Graphics2D graph = (Graphics2D)grf;
        
        //Sets the value of a single preference for the rendering algorithms.
        graph.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        
        // get width and height
        int width = getWidth();
        int height = getHeight();
        
        // draw graph
        graph.draw(new Line2D.Double(marg, marg, marg, height-marg));
        graph.draw(new Line2D.Double(marg, height-marg, width-marg, height-marg));
        
        //find value of x and scale to plot points
        double x = (double)(width-2*marg)/(cord.length-1);
        double scale = (double)(height-2*marg)/getMax();
        
        //set color for points
        graph.setPaint(Color.RED);
        
        // set points to the graph
        for(int i=0; i<cord.length; i++){
            double x1 = marg+i*x;
            double y1 = height-marg-scale*cord[i];
            graph.fill(new Ellipse2D.Double(x1-2, y1-2, 4, 4));
        }
    }
    
    //create getMax() method to find maximum value
    private int getMax(){
        int max = -Integer.MAX_VALUE;
        for(int i=0; i<cord.length; i++){
            if(cord[i]>max)
                max = cord[i];
           
        }
        return max;
    }       
    
    //main() method start
    public static void main(String args[]){
    	//create an instance of JFrame class
    	JFrame frame = new JFrame();
    	// set size, layout and location for frame.
    	frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    	frame.add(new PlotExample());
    	frame.setSize(400, 400);
    	frame.setLocation(200, 200);
    	frame.setVisible(true);
    }
}

Output:

Description

In the above code, PlotExample is the class which we create for plotting the graph, cord is an array of numbers which are treated as coordinates to be plot on the graph. We also extend the JPanel class for representing the graph.

Note: By default, the layout of the Panel is Flow-Layout but we can set any other layout also such as grid layout, card layout, box layout, and border layout etc.

We use super.paintComponent(g) to draw the graph on JPanel. In our code, we use Super keyword to call parent class method or constructor. In our case, the Super method calls the paintComponent(g) method of the JPanel class.

We use Graphic 2D class(a fundamental class for two dimensional shapes) that extends Graphics class for providing control over geometry.

We use RenderingHints which are basically suggestions for the Java 2D about how it should perform its rendering. In simple words, rendering means a way something is performed.

We use setRenderingHints() method to set new hints and replace the old ones.

We use Antialiasing to make smooth the jagged edges in case when the resolution is very low.

In order to draw lines representing the x-axis and y-axis, we need four coordinates, i.e., x1, y1, x2, and y2. In our code, we use g1.draw() method to draw lines.

We use the setpaint() method for setting the color of the points which we plot on the graph.

We use the for loop in our code and inside of that loop, we use coordinates.length() method for finding the length of the coordinates array.

We use the component's getWidth() and getHeight() methods of component that returns the height and width of the component.

We use x1 and y1 variables to plot the points with respect to the size of the component instead of the cartesian plane.

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