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Groovy example source code file (nbody.java)

This example Groovy source code file (nbody.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Groovy tags/keywords

body, body, days_per_year, days_per_year, decimalformat, nbodysystem, nbodysystem, numberformat, pi, solar_mass, solar_mass, text

The Groovy nbody.java source code

/* The Computer Language Shootout
   http://shootout.alioth.debian.org/

   contributed by Mark C. Lewis
*/

import java.text.*;

public final class nbody {
   private static final NumberFormat nf = new DecimalFormat("#0.000000000");

	public static void main(String[] args) {
	   int n = Integer.parseInt(args[0]);
	   
		NBodySystem bodies = new NBodySystem();
		
		System.out.println(nf.format(bodies.energy()) );
		for (int i=0; i<n; ++i) {
		   bodies.advance(0.01);
		}
		System.out.println(nf.format(bodies.energy()) );		
	}
}


final class NBodySystem {		
	private Body[] bodies;
	   	  	
	public NBodySystem(){			
		bodies = new Body[]{
		      Body.sun(),		
		      Body.jupiter(),
		      Body.saturn(),
		      Body.uranus(),
		      Body.neptune()		      		      		      
		   };
		
		double px = 0.0;
		double py = 0.0;	
		double pz = 0.0;				
		for(int i=0; i < bodies.length; ++i) {			   		         					
			px += bodies[i].vx * bodies[i].mass;
			py += bodies[i].vy * bodies[i].mass;		
			pz += bodies[i].vz * bodies[i].mass;				
		}		
		bodies[0].offsetMomentum(px,py,pz);
	}
						   	
	public void advance(double dt) {
	   double dx, dy, dz, distance, mag;	
	
		for(int i=0; i < bodies.length; ++i) {
			for(int j=i+1; j < bodies.length; ++j) {	
				dx = bodies[i].x - bodies[j].x;
				dy = bodies[i].y - bodies[j].y;
				dz = bodies[i].z - bodies[j].z;
				
				distance = Math.sqrt(dx*dx + dy*dy + dz*dz);				   
				mag = dt / (distance * distance * distance);
				
				bodies[i].vx -= dx * bodies[j].mass * mag;
				bodies[i].vy -= dy * bodies[j].mass * mag;
				bodies[i].vz -= dz * bodies[j].mass * mag;
				
				bodies[j].vx += dx * bodies[i].mass * mag;
				bodies[j].vy += dy * bodies[i].mass * mag;
				bodies[j].vz += dz * bodies[i].mass * mag;
			}
		}		
		
		for(int i=0; i < bodies.length; ++i) {
			bodies[i].x += dt * bodies[i].vx;
			bodies[i].y += dt * bodies[i].vy;
			bodies[i].z += dt * bodies[i].vz;
		}		
	}			
	
	public double energy(){		
		double dx, dy, dz, distance;	
		double e = 0.0;		   
		
		for (int i=0; i < bodies.length; ++i) {
			e += 0.5 * bodies[i].mass * 
			   ( bodies[i].vx * bodies[i].vx 
			   + bodies[i].vy * bodies[i].vy 
			   + bodies[i].vz * bodies[i].vz );
			   
			for (int j=i+1; j < bodies.length; ++j) {
				dx = bodies[i].x - bodies[j].x;
				dy = bodies[i].y - bodies[j].y;
				dz = bodies[i].z - bodies[j].z;
				
				distance = Math.sqrt(dx*dx + dy*dy + dz*dz);
				e -= (bodies[i].mass * bodies[j].mass) / distance;
			}
		}
		return e;
	}		      	   	   	      	   		   														           		
}


final class Body {
   static final double PI = 3.141592653589793;	
   static final double SOLAR_MASS = 4 * PI * PI;
	static final double DAYS_PER_YEAR = 365.24;

	public double x, y, z, vx, vy, vz, mass;
	
	public Body(){}	
	
	static Body jupiter(){
	   Body p = new Body();
	   p.x = 4.84143144246472090e+00;
	   p.y = -1.16032004402742839e+00;
	   p.z = -1.03622044471123109e-01;
	   p.vx = 1.66007664274403694e-03 * DAYS_PER_YEAR;
	   p.vy = 7.69901118419740425e-03 * DAYS_PER_YEAR;
	   p.vz = -6.90460016972063023e-05 * DAYS_PER_YEAR;
	   p.mass = 9.54791938424326609e-04 * SOLAR_MASS;	   	   	   
	   return p;
	}	
	
	static Body saturn(){
	   Body p = new Body();
	   p.x = 8.34336671824457987e+00;
	   p.y = 4.12479856412430479e+00;
	   p.z = -4.03523417114321381e-01;
	   p.vx = -2.76742510726862411e-03 * DAYS_PER_YEAR;
	   p.vy = 4.99852801234917238e-03 * DAYS_PER_YEAR;
	   p.vz = 2.30417297573763929e-05 * DAYS_PER_YEAR;
	   p.mass = 2.85885980666130812e-04 * SOLAR_MASS;	   	   	   
	   return p;
	}	
	
	static Body uranus(){
	   Body p = new Body();
	   p.x = 1.28943695621391310e+01;
	   p.y = -1.51111514016986312e+01;
	   p.z = -2.23307578892655734e-01;
	   p.vx = 2.96460137564761618e-03 * DAYS_PER_YEAR;
	   p.vy = 2.37847173959480950e-03 * DAYS_PER_YEAR;
	   p.vz = -2.96589568540237556e-05 * DAYS_PER_YEAR;
	   p.mass = 4.36624404335156298e-05 * SOLAR_MASS;		   	   	   
	   return p;
	}		

	static Body neptune(){
	   Body p = new Body();
	   p.x = 1.53796971148509165e+01;
	   p.y = -2.59193146099879641e+01;
	   p.z = 1.79258772950371181e-01;
	   p.vx = 2.68067772490389322e-03 * DAYS_PER_YEAR;
	   p.vy = 1.62824170038242295e-03 * DAYS_PER_YEAR;
	   p.vz = -9.51592254519715870e-05 * DAYS_PER_YEAR;
	   p.mass = 5.15138902046611451e-05 * SOLAR_MASS;	   	   	   
	   return p;
	}
	
	static Body sun(){
	   Body p = new Body();
	   p.mass = SOLAR_MASS;	   	   	   
	   return p;
	}			
	
	Body offsetMomentum(double px, double py, double pz){
	   vx = -px / SOLAR_MASS;
	   vy = -py / SOLAR_MASS;
	   vz = -pz / SOLAR_MASS;	   
	   return this;   
	}			           			
}

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