有人可以解釋這種奇怪的toString行爲嗎？

Question

我寫了一個代表Polynom的類。 coefficients保持係數。 unknown擁有代表未知數的char。

我有什麼期望時coefficients包含[2,2,3]："2x^2 + 2x + 3"

現實："122.0^2 + 2.0x + 3.0x"

代碼：

public class Polynom implements Comparable<Polynom> { 
private ArrayList<Number> coefficients; 
private int degree = 0; 
private char unknown = 'x'; 
private String name = "P(x)"; 

public Polynom() { 
    this("P(x)", 'x', null); 
} 


/** 
* Accepts Format: A1x^n + A2x^n-1 + ... + A(n-1)^1 + An 
* @param coefficients - Number array of coefficients (varargs) 
*/ 
@SafeVarargs 
public Polynom(Number... coefficients) { 
    this("P(x)", 'x', Arrays.asList(coefficients)); 
} 

public Polynom(String name, char unknown, List<Number> coefficients) { 
    this.name = name; 
    if (coefficients != null) 
     this.coefficients = new ArrayList<>(coefficients); 
    else 
     this.coefficients = new ArrayList<>(); 
    this.unknown = unknown; 
    this.degree = this.coefficients.size(); 
} 

@Override 
public String toString() { 
    StringBuilder sb = new StringBuilder(name + '='); 
    int cdeg = degree - 1; 
    for (Number a : coefficients) { 
     double absvalue = Math.abs(a.doubleValue()); 
     String sign = (a.doubleValue() > 0 ? " + " : " - "); 
     if (absvalue > 1) 
      if (cdeg != degree - 1) 
       sb.append(sign + absvalue + unknown 
         + (cdeg > 1 ? "^" + cdeg : "")); 
      else 
       sb.append(absvalue + unknown + (cdeg > 1 ? "^" + cdeg : "")); 
     else if (absvalue == 1) 
      if (cdeg != degree - 1) 
       sb.append(sign + unknown + (cdeg > 1 ? "^" + cdeg : "")); 
      else 
       sb.append(unknown + (cdeg > 1 ? "^" + cdeg : "")); 
     else 
      sb.append(sign + absvalue); 
     cdeg--; 
    } 
    return sb.toString(); 
} 

@Override 
public int compareTo(Polynom o) {...} 

@Override 
public boolean equals(Object o) {...} 
} 

public static void main(String[] args) { 
    Polynom p1,p2; 
    p1 = new Polynom(1,-2,3); 
    p2 = new Polynom(2,2,3); 
    System.out.println(p1+"\n"+p2); 
} 

Answer 1

你的問題是，你正在試圖連接一char到number，由於沒有涉及String，所以導致增加而不是串聯。

當您將追加2+unknown你StringBuilder，要附加2+'x'，這是122（因爲120是字符「X」的數值）。

將您的未知數從char更改爲String。

String unknown = "x"; 

這就是你需要改變的一切。