我对java比较新，所以如果我在这里遗漏了一些明显的东西，我也不会感到惊讶。无论如何，我做了一个代码，使用Bisection方法找到多项式的根。我认为该程序一切顺利，直到我将它从notepad ++粘贴到命令提示符，在使用javac编译它之后，我最终得到了一堆“class，interface或enum expected”错误。代码本身的一切似乎都很好，所以我推断出我已经犯了以下两个错误之一：当我复制并粘贴到命令提示符时出现了错误，或者我确实在我的代码中创建了一个错误我没抓到。有人能告诉我我做错了什么吗？它可能是一个小修复，但我只是不知道如何更改它以使我的代码工作。这是代码：
import java.util.*;
class Roots {
public static int degree;
public static double[] coArrayC;
public static double[] coArrayD;
public static int coeffVal;
public static void main( String[] args ){
double resolution = 0.01;
double tolerance = 0.0000001;
double threshold = 0.001;
double rightEndPt;
double leftEndPt;
int polyRootPointer = 0;
int diffRootPointer = 0;
boolean rootAns = false;
Scanner sc = new Scanner(System.in);
System.out.println();
System.out.print("Enter the degree: "); //prompts user to enter the correct degree of the polynomial
degree = sc.nextInt();
coeffVal = degree + 1; //the coefficient is one more than the number of degrees
System.out.print("Enter " + coeffVal + " coefficients: "); //adds in the value of the polynomial coefficient in to the line that prompts the user to specify which coefficients are in the function
double[] coefficients = new double[coeffVal]; //initialization of array, a bunch of doubles that represent the coefficients of the user's polynomial
coArrayC = new double[coeffVal]; //naming the array
double[] rootArray = new double[degree];//another array for the degrees of the polynomial
coArrayD = new double[coeffVal]; //and assigning it a name
for(int i = 0; i < coeffVal; i++) {
coefficients[i] = sc.nextDouble();
}
System.out.print("Enter the right and left endpoints, in that order: "); //prompts user to enter the interval limits
rightEndPt = sc.nextDouble();
leftEndPt = sc.nextDouble();
diff(coefficients); //calculates coefficients of derivative polynomial
for (double i = leftEndPt; i < rightEndPt-resolution; i = i + resolution){ //
if (isPositive(coArrayD, i) != isPositive(coArrayD, i+resolution) || isPositive(coArrayD, i) == 0) {
rootArrayDeriv[diffRootPointer] = findRoot(coArrayD, i, i+resolution, tolerance);
diffRootPointer++;
}
}
for (int i = 0; i < rootArrayDeriv.length; i++) {
double tempValue;
tempValue = poly(coefficients, rootArrayDeriv[i]);
tempValue = Math.abs(tempValue);
if (tempValue < threshold) {
rootArray[polyRootPointer] = rootArrayDeriv[i];
polyRootPointer++;
rootAns = true;
}
}
for (double i = leftEndPt; i < rightEndPt-resolution; i = i + resolution){
if (isPositive(coefficients, i) != isPositive(coefficients, i+resolution) || isPositive(coefficients, i) == 0) {
rootArray[polyRootPointer] = findRoot(coefficients, i, i+resolution, tolerance);
polyRootPointer++;
rootAns = true;
}
}
//Arrays.sort(rootArray); //sorts array from lowest to highest
if (rootAns == true) {
System.out.println("Sorry - no roots were found in the specified interval.");
}
}
} else {
for (int i = 0; i < rootArray.length; i++) {
if (rootArray[i] != 0.0) {
System.out.printf("Root found at %.5f\n :" Arrays.sort(rootArray[i])); //if roots are found, list them as an output, with five decimal places of accuracy
}
}
static double poly(double[] C, double x){
double polySum = 0;
coArrayC[0] = C[0];
for (int i = 1; i < coArrayC.length; i++){
coArrayC[i] = C[i]*(Math.pow(x, i)); //multiplies each coefficient by the designated power of X
}
for (int i = 0; i < coArrayC.length; i++){
polySum = polySum + coArrayC[i]; //accumulates the sum of of all the terms, after the coeff. were multiplied to their respective powers.
}
return(polySum);
}
static double[] diff(double[] C){
for (int i = 0; i < degree; i++){
coArrayD[i] = (i+1)*C[i+1]; //newly allocated array D containing coeff. of the polynomial that is the derivative of the polynomial with coeff. array C.
}
return(coArrayD);
}
static double findRoot(double[] C, double a, double b, double tolerance){ //using bisection method; similar to findRoot.java in cmps webpage.
double root = 0.0 , residual;
while ( Math.abs(b - a) > tolerance ) {
root = (a + b) / 2.0;
residual = poly(C, root);
if (poly(C, a) < 0 && poly(C, b) < 0) {
if (residual > 0)
b = root;
else
a = root;
} else if (poly(C, a) > 0 && poly(C, b) > 0) {
if (residual > 0)
a = root; //replace left endpoint
else
b = root; //replace right endpoint
}
}
return(root);
}
static int isPositive(double[] C, double a){
double endpointTempA;
endpointTempA = poly(C, a);
if (endpointTempA < 0) {
return(1);
} else if (endpointTempA > 0) {
return(2);
} else {
return(0);
}
}
}
答案 0 :(得分：0)
这里有两个}太多了：
if (rootAns == true) {
System.out.println("Sorry - no roots were found in the specified interval.");
}
}
} else {
如果您正确缩进代码，则更容易看到这些类型的错误。删除不属于那里的两个}：
if (rootAns == true) {
System.out.println("Sorry - no roots were found in the specified interval.");
} else {
这里还缺少,，你不应该将double传递给Arrays.sort，而是整个数组
System.out.printf("Root found at %.5f\n :"Arrays.sort(rootArray[i]));
应该是：
System.out.printf("Root found at %.5f\n :", Arrays.sort(rootArray));
缺少}。
不是一次编写整个程序然后尝试编译它，而是一点一点地编写它，并在每次有一个完整的方法时编译它。这样你就可以避免让一大堆小错误让你迷惑。