Java-格式化Double數據類型，出現錯誤

Question

這是我的作業分配的代碼。 遲來了很久，我在這方面做得不好，但是想嘗試自己的錯誤和問題，以便在學校里做得更好。 但無論如何：

  double x1, y1, x2, y2, x3, y3; // Three points for three vertices. 
                                 // (x1, y1), (x2, y2), (x3, y3)

  Scanner input = new Scanner(System.in);

  // The program asks the user what the name of the triangle is. Then the program
  // asks the user for the cordinates of each point.
  System.out.print("Enter a three letter name for the triangle: ");
  String triangleName = input.next();
  System.out.print("Coordinates of vertex " + triangleName.substring(0,1).toUpperCase() + ":");
  x1 = input.nextDouble();
  y1 = input.nextDouble();
  System.out.print("Coordinates of vertex " + triangleName.substring(1,2).toUpperCase() + ":");
  x2 = input.nextDouble();
  y2 = input.nextDouble();
  System.out.print("Coordinates of vertex " + triangleName.substring(2,3).toUpperCase() + ":");
  x3 = input.nextDouble();
  y3 = input.nextDouble();

  double a, b, c; // These values will serve as the three side
                  // lengths between the points.

  // The program displays side lengths in this block.
  System.out.println("--- Side lengths ---");
  a = Math.sqrt(Math.pow(x2-x1, 2) + Math.pow(y2-y1, 2));
  System.out.printf(triangleName.substring(0,1).toUpperCase()
                      + triangleName.substring(1,2).toUpperCase() + ":"
                      + "%.3f", a);
  System.out.println();
  b = Math.sqrt(Math.pow(x3-x2, 2) + Math.pow(y3-y2, 2));
  System.out.printf(triangleName.substring(1,2).toUpperCase()
                       + triangleName.substring(2,3).toUpperCase() + ":"
                       + "%.3f", b);
  System.out.println();
  c = Math.sqrt(Math.pow(x3-x1, 2) + Math.pow(y3-y1, 2));
  System.out.printf(triangleName.substring(2,3).toUpperCase()
                       + triangleName.substring(0,1).toUpperCase() + ":"
                       + "%.3f", c);
  System.out.println();

  double perimeter, area, xCentroid, yCentroid, inRadius, inArea, semiPerimeter, triangleHeight, triangleBase;

  // The program displays other measures in this block.
  System.out.println("--- Other measures ---");
  perimeter = a + b + c;
  System.out.printf("Perimeter         = " + "%.3f", perimeter);
  System.out.println();
  triangleHeight = y3 - 0.1;
  triangleBase = x2 - x1;
  area = (triangleHeight * triangleBase) / 2;
  System.out.printf("Area              = " + "%.3f", area);
  System.out.println();
  xCentroid = (x1 + x2 + x3) / 3;
  yCentroid = (y1 + y2 + y3) / 3;
  System.out.printf("Centroid          = ( " + "%.3f", xCentroid + ", " + yCentroid + ")");
  System.out.println();
  semiPerimeter = 0.5 * perimeter;
  inRadius = area / semiPerimeter;
  System.out.format("Incircle radius   = " + "%.3f", inRadius);
  System.out.println();
  inArea = Math.PI * Math.pow(inRadius, 2);
  System.out.format("Incircle area     = " + "%.3f", inArea);
  System.out.println();

代碼中的問題在於分別格式化xCentroid和yCentroid值的行。 我收到一條錯誤消息"java.util.IllegalFormatConversionException: f != java.lang.String" 。 程序中的數學運行正常，也可以運行。 我已刪除語句中的“％.3f”，以查看是否獲得正確答案，即可以。 只是這種格式讓我很生氣。 請回復，並提供幫助。 我待會兒，會耐心的。

新代碼（固定）：

  System.out.print("Centroid          = ");
  System.out.print("(");
  System.out.printf("%.3f", xCentroid);
  System.out.print(", ");
  System.out.printf("%.3f", yCentroid);
  System.out.print(")");
  System.out.println();

Answer 1

在這段代碼中

System.out.printf("Centroid          = ( " + "%.3f", xCentroid + ", " 
                                                        + yCentroid + ")");

特別是這個

xCentroid + ", " + yCentroid + ")"

不會是數字，而是一個字符串

我想你想要的是

System.out.printf("Centroid          = (%.3f)", xCentroid + yCentroid);