java 报错无法访问语句

Question

import java.util.Random;public class Question4{ public static void main(String[] args) { float x1=0; float x2=0; System.out.println("The coefficients of the function f(x)=a*x^2+b*x+c are:"); Random randomObj=new Random(); float a =randomObj.nextFloat(); System.out.println("a="+a); float b =randomObj.nextFloat(); System.out.println("b="+b); float c =randomObj.nextFloat(); System.out.println("c="+c); double d =Math.pow(b,2)-4*a*c; System.out.println("The equation f(x)=0 is quadratic with complex solutions:"); if (a==0) { if (b==0) { if(c==0) System.out.print( "Equation is trivial"); else System.out.print("No solution"); return; } else { System.out.print(x1=x2=-c/b); return; } } else { if (d<0) { System.out.println((double)x1==(-b+Math.sqrt(Math.pow(b,2)-4*a*c))/2/a); System.out.println((double)x2==(-b-Math.sqrt(Math.pow(b,2)-4*a*c))/2/a); return; } if(d==0) System.out.println(x1=x2=-b/(2*a)); return; if(d>0) { System.out.println((double)x1==(-b+Math.sqrt(d)/(2*a))); System.out.println((double)x2==(-b-Math.sqrt(d)/(2*a))); } } if (x1!=x2) { System.out.println("Check:"); System.out.println("\t"+"f(x1)="+Math.pow((a*x1),2)+b*x1+c+"\n"+"f(x2)="+Math.pow((a*x2),2)+b*x2+c); return; } else System.out.println(" ")；
}
}

Answer 1

if(d==0)
System.out.println(x1=x2=-b/(2*a));
return;
这几句，没有加括号，所以return已经脱离了if语句了，程序执行到这里就返回了，后面的语句无法访问了。改成这样就可以了：

if(d==0){
System.out.println(x1=x2=-b/(2*a));
return;}

Answer 2

 if(d==0)
   System.out.println(x1=x2=-b/(2*a));
 return; 

// 因为上面的return,以下代码永远不会运行,是不是应该改成
// if(d==0) {
//   System.out.println(x1=x2=-b/(2*a));
//   return; 
// }
 
 if(d>0)
 {

追问

运行起来还是不对的，怎么会出现false呢？

追答

 是不是解一元二次方程的?我把程序稍微修改了下.字数太多,只放修改的部分了

  } else {
   if (d < 0) {
    System.out.println("No solution");
    return;
   }
   if (d == 0) {
    System.out.println(x1 = x2 = -b / (2 * a));
    return;
   }
   if (d > 0) {
    System.out.println(
      x1 = (float) (-b + Math.sqrt(Math.pow(b, 2) - 4 * a * c)) / 2 / a);
    System.out.println(
      x2 = (float) (-b - Math.sqrt(Math.pow(b, 2) - 4 * a * c)) / 2 / a);
   }
  }
  if (x1 != x2) {
   System.out.println("Check:");
   System.out.println("\t"
     + "f(x1)=" + (a * Math.pow(x1, 2) + b * x1 + c) + "\n\t"
     + "f(x2)=" + (a * Math.pow(x2, 2) + b * x2 + c));
   return;
  } else
   System.out.println(" ");
 }
}

Answer 3

if(d==0)
System.out.println(x1=x2=-b/(2*a));
return;

这一行没加大括号，所以相当于
if(d==0){
System.out.println(x1=x2=-b/(2*a));
}
return;

在执行if(d > 0)之前就return了，所以if(d > 0)是执行不到的代码，报错了。

Answer 4

import java.util.Random;
public class Question4
{
public static void main(String[] args)
{
float x1=0;
float x2=0;
System.out.println("The coefficients of the function f(x)=a*x^2+b*x+c are:");
Random randomObj=new Random();
float a =randomObj.nextFloat();
System.out.println("a="+a);
float b =randomObj.nextFloat();
System.out.println("b="+b);
float c =randomObj.nextFloat();
System.out.println("c="+c);
double d =Math.pow(b,2)-4*a*c;
System.out.println("The equation f(x)=0 is quadratic with complex solutions:");
if (a==0)
{
if (b==0)
{
if(c==0)
System.out.print( "Equation is trivial");
else
System.out.print("No solution");
return;
}
else
{
System.out.print(x1=x2=-c/b);
return;
}
}
else
{
if (d<0)
{
System.out.println((double)x1==(-b+Math.sqrt(Math.pow(b,2)-4*a*c))/2/a);
System.out.println((double)x2==(-b-Math.sqrt(Math.pow(b,2)-4*a*c))/2/a);
return;
}
if(d==0)
System.out.println(x1=x2=-b/(2*a));
// return;
if(d>0)
{
System.out.println((double)x1==(-b+Math.sqrt(d)/(2*a)));
System.out.println((double)x2==(-b-Math.sqrt(d)/(2*a)));

}
if (x1!=x2)
{ System.out.println("Check:");
System.out.println("\t"+"f(x1)="+Math.pow((a*x1),2)+b*x1+c+"\n"+"f(x2)="+Math.pow((a*x2),2)+b*x2+c);
return;
}
else
System.out.println(" ");
}
}
}

return 那里有问题，return后面不能有算法了！

Answer 5

好奇葩错！！！