Question

我正在编写一个计算3度多项式根的算法，我的App崩溃了。我将整个代码复制到NetBeans，它工作正常。这是android studio的代码：

public class poly3_next extends Activity{

//public final static String EXTRA_MESSAGE = "com.michniewicz.jan.mathcalcalpha.poly3_next";

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_poly3_next);


    //getting data from previous activity

    String value="";
 Bundle extras = getIntent().getExtras();
        if (extras != null) {
            value = extras.getString("pass");
        }
        final String finalValue = value;



    final TextView display1 = (TextView) findViewById(R.id.poly3_next_tbe1);
    final TextView display2 = (TextView) findViewById(R.id.poly3_next_tbe2);
    final TextView display3 = (TextView) findViewById(R.id.poly3_next_tbe3);

    String[] coefficients=new String[4];
    int k=0;
    int pointer2=0;
    for(int pointer=0; pointer<finalValue.length();pointer++){

        if((finalValue.substring(pointer,pointer+1)).equals("@")){
            coefficients[k]=finalValue.substring(pointer2,pointer);
            pointer2=pointer+1;
            k++;
        }
    }



  double cf0=Double.parseDouble(coefficients[3]);
  double cf1=Double.parseDouble(coefficients[2]);
   double cf2=Double.parseDouble(coefficients[1]);
   double cf3=Double.parseDouble(coefficients[0]);

    double solution1=0,solution2=0,solution3=0;



   solution1=PolySolver(cf3,cf2,cf1,cf0)[0];
  display1.setText(""+solution1);
   solution2=PolySolver(cf3,cf2,cf1,cf0)[1];
    display2.setText(""+solution2);
   solution3=PolySolver(cf3,cf2,cf1,cf0)[2];
    display3.setText(""+solution3);


        }

解决工作正常的功能，但我会发布以防万一：

 public static double[] PolySolver(double c3,double c2,double c1,double c0){
    double[] roots=new double[3];
    int k=0;
    roots[0]=258.74;
    roots[1]=258.74;
    roots[2]=258.74;
    double x0=-1;
    double x1=1;
    for(int i=0; i <c0; i++ ){
        double Rawroot=SecantMethod(c3,c2,c1,c0,x0,x1);
        String sroot=""+Rawroot;
        if(sroot.length()>8){
            sroot=sroot.substring(0, 8);
        }
        double root=Double.parseDouble(sroot);
        if(k<=2&& root!=roots[2]&&root!=roots[1]&& root!=roots[0]){
            roots[k]=root;
            if(k==2){
                return roots;
            }
            k++;

        }

        x0=x0-1;
        x1=x1+1;
    }
    return roots;
}


public static double SecantMethod(double c3,double c2,double c1,double c0,double x0,double x1)
{
// Local variables
        double x, // Calculated value of x at each iteration
                f0, // Function value at x0
                f1, // Function value at x1
                fx, // Function value at calculated value of x
                root, // Root, if within desired tolerance
                // x0=-1, //First guess
                //x1=c0, //second guess
                tol=0.000000001, //accuracy
                n=2000; //number of times executed
// Set initial function values
        f0 = Function(c3,c2,c1,c0,x0);
        f1 = Function(c3,c2,c1,c0,x1);
// Loop for finding root using Secant Method
        for(int i = 0; i < n; i++)
        {
            x = x1 - f1 * ((x1 - x0) / (f1 - f0));
            fx = Function(c3,c2,c1,c0,x);
            x0 = x1;
            x1 = x;
            f0 = f1;
            f1 = fx;
// Check whether calculated value is within tolerance
            if(Math.abs(x1 - x0) < tol)
            {
                root = x1;

                return root;
            } // end if
        } // end for
        return x1;
    }
    public static double Function(double c3, double c2, double c1,double c0,double x){
        double y=c3*(Math.pow(x, 3))+c2*(Math.pow(x, 2))+c1*x+c0;
        return y;
    }

}

我测试了所有内容，似乎导致应用崩溃的行是：

double cf0=Double.parseDouble(coefficients[3]);
      double cf1=Double.parseDouble(coefficients[2]);
       double cf2=Double.parseDouble(coefficients[1]);
       double cf3=Double.parseDouble(coefficients[0]);

Answer 1

尝试改变这个：

for(int pointer=0; pointer<finalValue.length();pointer++){

    if((finalValue.substring(pointer,pointer+1)).equals("@")){
        coefficients[k]=finalValue.substring(pointer2,pointer);
        pointer2=pointer+1;
        k++;
    }
}

你写的if中的

finalValue.substring(pointer, pointer+1).equal... 评论此行并尝试运行。它崩溃了，因为在最后一个循环中，指针+ 1的值为空。

例如：

for(max 5 time){
  substring(0, 1)
  substring(1, 2)
  ....
  substring(5, 6!)
}

应用程序因变量声明而崩溃

1 个答案: