Project0 Nbody-simulation

讲义：NBody Simulation | CS 61B Spring 2018

为什么使用Git命令+javac？？

答：
这样可以单独的编译和运行某一个程序，而IDE编译一个程序的时候还会编译其它的程序，会很烦人

翻译时绕过数学公式

goole浏览器按F12进入网页控制台，输入$('math, .math, .MathJax').attr('translate','no');

javac编译的时候注意事项

javac -encoding UTF-8 Planet.java TestCalcForceExertedBy.java	//有中文
javac TestCalcForceExertedBy.java	//无中文

增强的for循环

public class EnhancedForBreakDemo {
    public static void main(String[] args) {
        String[] a = {"cat", "dog", "laser horse", "ketchup", "horse", "horbse"};

        for (String s : a) {
            for (int j = 0; j < 3; j += 1) {
                System.out.println(s);
                if (s.contains("horse")) {
                    break;
                }                
            }
        }
    }
}

可视化代码，超好用
Online Java Compiler, Visual Debugger, and AI Tutor - Learn Java programming by visualizing code

Planets类

import java.security.PublicKey;

public class Planet {
    public double xxPos;
    public double yyPos;
    public double xxVel;
    public double yyVel;
    public double mass;
    public String imgFileName;
    public Planet(double xP,double yP,double xV,double yV,double m,String img){
            this.xxPos=xP;
            this.yyPos=yP;
            this.xxVel=xV;
            this.yyVel=yV;
            this.mass=m;
            this.imgFileName=img;
    }
//    public Planet(){
//        this(0,0,0,0,0,null);
//    }
    public Planet(Planet p){
        this(p.xxPos,p.yyPos,p.xxVel,p.yyVel,p.mass,p.imgFileName);
    }
    /*计算两个物体之间的距离的平方*/
    public double calcDistance(Planet other){
        return Math.sqrt((this.xxPos-other.xxPos)*(this.xxPos- other.xxPos)+(this.yyPos-other.yyPos)*(this.yyPos-other.yyPos));
    }
    /*计算两个物体之间的受力，牛顿万有引力*/
    public double calcForceExertedBy(Planet other){
        double G=6.67e-11;
        return (G*(this.mass*other.mass))/(this.calcDistance(other)*this.calcDistance(other));
    }
    //this代表受力的物体，other代表施力的物体
    //X分力
    public double calcForceExertedByX(Planet other){
        double F=this.calcForceExertedBy(other);
        double r=this.calcDistance(other);
        return F*(other.xxPos-this.xxPos)/r;
    }
    //Y方向上的分力
    public double calcForceExertedByY(Planet other){
        double F=this.calcForceExertedBy(other);
        double r=this.calcDistance(other);
        return F*(other.yyPos-this.yyPos)/r;
    }
    //计算受力物体受其他物体X方向上的力
    public double calcNetForceExertedByX(Planet[] planets){
        double xNetForce=0.0;
        for(Planet p:planets){
            if(!this.equals(p))
                xNetForce+=this.calcForceExertedByX(p);
        }
        return xNetForce;
    }
    //计算受力物体受其它物体Y方向的力
    public double calcNetForceExertedByY(Planet[] planets){
        double yNetForce=0;
        for(Planet p:planets){
            if(!this.equals(p))
                yNetForce+=this.calcForceExertedByY(p);
        }
        return yNetForce;
    }
    //更新速度，牛顿第二定理
    //已知x,y方向的分力以及作用的时间，求出变化后的速度

    public void update(double time,double xForce,double yForce){
        //由F=ma先求出a，然后v=v0+a*t;
        double ax=xForce/this.mass;
        double ay=yForce/this.mass;
        this.xxVel=this.xxVel+ax*time;
        this.yyVel=this.yyVel+ay*time;
        //讲义给的公式：p_new=p_old+v_new*dt
        //我高中学的：p_new=p_old+0.5*a*t*t;算了按讲义来吧
        this.xxPos=this.xxPos+this.xxVel*time;
        this.yyPos=this.yyPos+this.yyVel*time;
    }
    public void draw(){
        StdDraw.picture(this.xxPos,this.yyPos,"images/"+this.imgFileName);
    }
}

public class NBody {
    //返回宇宙的半径
    public static double readRadius(String Filename){
        In in=new In(Filename);
        int N=in.readInt();
        return in.readDouble();
    }
    //返回行星数组
    public static Planet[] readPlanets(String Filename){
        In in=new In(Filename);
        int N=in.readInt();
        Planet[] planets=new Planet[N];
        double radius=in.readDouble();
        for(int i=0;i<N;i++){
            double xxPos =in.readDouble() ,
                    yyPos = in.readDouble(),
                    xxVel = in.readDouble(),
                    yyVel = in.readDouble(),
                    mass =in.readDouble();
            String imageFile=in.readString();
            Planet p=new Planet(xxPos,yyPos,xxVel,yyVel,mass,imageFile);
            planets[i]=p;
        }
        return planets;
    }

    public static void main(String[] args){
        double T=Double.parseDouble(args[0]);
        double dt=Double.parseDouble(args[1]);
        String filename="./"+args[2];
        Double Radius=readRadius(filename);
        Planet[] planets=readPlanets(filename);
        int N=planets.length;
        StdDraw.setXscale(-Radius,Radius);
        StdDraw.setYscale(-Radius,Radius);
        StdDraw.enableDoubleBuffering();
        //StdDraw.picture(0,0,"images/starfield.jpg");
        //for(int i=0;i<N;i++)
        //    planets[i].draw();

        double t=0;
        while(t<=T){
            double[] xForces=new double[N];
            double[] yForces=new double[N];
            for(int i=0;i<N;i++){
                xForces[i]=planets[i].calcNetForceExertedByX(planets);
                yForces[i]=planets[i].calcNetForceExertedByY(planets);
            }
            for (int i=0;i<N;i++){
                planets[i].update(dt,xForces[i],yForces[i]);
            }
            StdDraw.picture(0,0,"images/starfield.jpg");
            for(int i=0;i<N;i++){
                planets[i].draw();
            }
            StdDraw.show();
            StdDraw.pause(10);
            t+=dt;
        }
        StdOut.printf("%d\n", planets.length);
        StdOut.printf("%.2e\n", Radius);
        for (int i = 0; i < planets.length; i++) {
            StdOut.printf("%11.4e %11.4e %11.4e %11.4e %11.4e %12s\n",
                    planets[i].xxPos, planets[i].yyPos, planets[i].xxVel,
                    planets[i].yyVel, planets[i].mass, planets[i].imgFileName);
        }
    }
}

恰当的位置绘制行星于背景

        StdDraw.setXscale(-Radius,Radius);
        StdDraw.setYscale(-Radius,Radius);
        StdDraw.picture(0,0,"images/starfield.jpg");
        for(int i=0;i<N;i++)
            planets[i].draw();