Processing is an open source programming language and environment for people who want to create images, animations, and interactions. Initially developed to serve as a software sketchbook and to teach fundamentals of computer programming within a visual context, Processing also has evolved into a tool for generating finished professional work. Today, there are tens of thousands of students, artists, designers, researchers, and hobbyists who use Processing for learning, prototyping, and production.

Create java project

• File > Import > General > File System

Import file system

• Browse the processing directory > choose core.jar > Finish

Import core.jar

• Right click on core.jar > build path > add to build path

Build path

import processing.core.*;

public class MyProcessingSketch extends PApplet {
  public void setup() {
    size(400,400);
    background(0);
  }

  public void draw() {
    stroke(200);
    if (mousePressed) {
      line(mouseX,mouseY,pmouseX,pmouseY);
    }
  }
}

Result