int無法解析爲變量java

Question

問題：當我試圖將int轉換爲double時，它顯示int無法解析爲變量的錯誤。該程序將輸入二次方程作爲輸入，並以此格式提取aX2-bX-c = 0的係數並求解二次方程。但是在從int到double的轉換中存在一些錯誤。

計劃：

public static String quad (final String equation) 
    { 
    final String regex = "([+-]?\\d+)X2([+-]\\d+)X([+-]\\d+)=0"; 
    Pattern pattern = Pattern.compile(regex); 


    Matcher matcher = pattern.matcher(equation); 

    if (matcher.matches()) { 
     int a1 = Integer.parseInt(matcher.group(1)); 
     int b1 = Integer.parseInt(matcher.group(2)); 
     int c1 = Integer.parseInt(matcher.group(3)); 

    // System.out.println("a=" + a + "; b=" + b + "; c=" + c); 
    } 
    double a = (double) a1; // error message a1 cannot resolve into variable 
    double b = (double) b1; // error message b1 cannot resolve into variable 
    double c = (double) c1; // error message c1 cannot resolve into variable 


    double r1 = 0; 
    double r2 = 0; 
    double discriminant = b * b - 4 * a * c; 
    if (discriminant > 0){ 

     // r = -b/2 * a; 

     r1 = (-b + Math.sqrt(discriminant))/(2 * a); 
     r2 = (-b - Math.sqrt(discriminant))/(2 * a); 

    // System.out.println("Real roots " + r1 + " and " + r2); 
    } 
    if (discriminant == 0){ 
     // System.out.println("One root " +r1); 

     r1 = -b/(2 * a); 
     r2 = -b/(2 * a); 

    } 
    if (discriminant < 0){ 
    // System.out.println(" no real root"); 

    } 

    String t1 = String.valueOf(r1); 
    String t2 = String.valueOf(r2); 
    String t3 ; 
    t3 = t1+" "+t2; 
    return t3; 

} 

Answer 1

，如果你想讓他們仍然在範圍上是塊結束後，您必須聲明if語句塊之前a1，b1和c1。

int a1 = 0; 
int b1 = 0; 
int c1 = 0; 
if (matcher.matches()) { 
    a1 = Integer.parseInt(matcher.group(1)); 
    b1 = Integer.parseInt(matcher.group(2)); 
    c1 = Integer.parseInt(matcher.group(3)); 
    // System.out.println("a=" + a + "; b=" + b + "; c=" + c); 
} 
double a = (double) a1; 
double b = (double) b1; 
double c = (double) c1; 

Answer 2

您可以直接使用雙打：

double a = 0.0, b = 0.0, c = 0.0; 
if (matcher.matches()) { 
    a = Double.parseDouble(matcher.group(1)); 
    b = Double.parseDouble(matcher.group(2)); 
    c = Double.parseDouble(matcher.group(3)); 
}