无法将自定义 object 数据类型的 ArrayList 转换为相应的常规数组

Question

正如标题所说，我无法将我的 ArrayList 转换为 Array。我的 ArrayList 的数据类型是 自定义 object 但我似乎无法找到我的问题所在。在程序运行之前，它给出的错误不会显示为问题。前两个 classes 是 objects，然后我有一个 class calle Tester，其中主要方法是。

Class出现错误的地方：

package backend;

import java.util.ArrayList;

public class Function {

Coefficient[] coefArray;
int constant;

public Function(ArrayList<Coefficient> coefFunction, int constant){
    Coefficient[] coefArray = (Coefficient[]) coefFunction.toArray();
    this.coefArray = sortArray(coefArray);
    this.constant = constant;
}

private Coefficient[] sortArray(Coefficient[] newArray){
    int tempPow = -1000000000;
    Coefficient[] sortedArray = new Coefficient[newArray.length];
    sortedArray = null;
    for(int i=0; isFull(sortedArray); i++){
        for(Coefficient coef : newArray){
            if(coef.pow>tempPow){
                tempPow = coef.pow;
                sortedArray[i] = coef;
            }
        }
    }
    return sortedArray;
}

private boolean isFull(Coefficient[] anArray){
    for(Coefficient i : anArray) {
        if(i == null) return true;
      }
     return false;
}

public String toString(){
    String compiledString="";
    for(Coefficient coef : coefArray){
        compiledString += coef.toString()+"+";
    }
    if(constant==0){
        //No constant there
    }else{
        compiledString = compiledString + constant;
    }
    return compiledString;
}
}

系数Class:

package backend;

public class Coefficient {

String stringVersion;
public int pow;
public int coefInteger;
public double coefDouble;

//Constructor for variable with a coefficient that is non-fractal and a power higher than 1
public Coefficient(int coef, int pow){
    this.coefInteger = coef;
    this.pow = pow;
    switch(coef){
        case 0:
            //Do nothing here
        case 1:
            this.stringVersion = "x^"+pow;
            break;
        default:
            this.stringVersion = coef+"x^"+pow;
            break;
    }
}

//Constructor for variable with a coefficient that is fractal and a power higher than 1
public Coefficient(double coef, int pow){
    this.coefDouble = coef;
    this.pow = pow;
    this.stringVersion = coef+"x^"+pow;
}

//Constructor for variable with a coefficient but no power
public Coefficient(double coef){
    this.coefDouble = coef;
    this.pow = 1;
    this.stringVersion = coef+"x";
}

//Constructor for variable with a coefficient but no power
public Coefficient(int coef){
    this.coefInteger = coef;
    this.pow = 1;
    this.stringVersion = coef+"x";
}

public String toString(){
    return stringVersion;
}
}

测试人员：

package backend;

import java.util.ArrayList;
import java.util.Scanner;

public class Tester {
public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    ArrayList<Coefficient> function = new ArrayList<Coefficient>();
    Coefficient xVal;
    Function printFunction;
    System.out.println("Enter the degree of the equation:");
    int pow = scan.nextInt();
    System.out.println("Enter the x components of the function in the order of coefficient then power. Enter constant last:");
        double coef = 0;
        while(pow>0){
            coef = scan.nextDouble();
            if(pow==1){
                if((int) coef == coef){
                    xVal = new Coefficient((int) coef);
                }else{
                    xVal = new Coefficient(coef);
                }
            }else{
                if((int) coef == coef){
                    xVal = new Coefficient((int) coef, pow);
                }else{
                    xVal = new Coefficient(coef, pow);
                }
            }
            function.add(xVal);
            pow--;
        }

        System.out.println("Enter the constant:");
        printFunction = new Function(function, scan.nextInt());
        System.out.println(printFunction.toString());


}
}

错误：

Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object;
cannot be cast to [Lbackend.Coefficient;
at backend.Function.<init>(Function.java:11)
at backend.Tester.main(Tester.java:36)

非常感谢任何帮助。如果您看到其他需要修复的地方，请指出。

Answer 1

错误在这一行：

Coefficient[] coefArray = (Coefficient[]) coefFunction.toArray();

如果你阅读 toArray() 的 javadoc，你会发现它 returns 一个 Object[]，你不能简单地转换为 Coefficient[].

改为使用toArray(T[] a):

Coefficient[] coefArray = coefFunction.toArray(new Coefficient[coefFunction.size()]);

免责声明：我没有审查您的其余代码，因此没有任何评论并不意味着其他一切都很好。

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