Java泛型和数字 [英] Java Generics and numbers

问题描述

试图看看我是否可以清理一些数学代码，主要是矩阵的东西，我试图使用一些Java泛型。我有以下方法：

  private< T> T [] [] zeroMatrix（int row，int col）{
 T [] [] retVal =（T [] []）new Object [row] [col]; （int j = col; j< col; j ++）{
 retVal [i] [j] = {
 for（int i = row; i } 
} 
 return retVal; 
} 
  

retVal [i] [j] = 0是引起我的那一行头痛。该行的目标是用T表示0初始化数组。我试图用它做各种事情：（T在类中定义为T扩展数字）

  retVal [i] [j] =（T）0; 
 retVal [i] [j] = new T（0）; 
  

唯一可行的是

  retVal [i] [j] =（T）new Object（0）; 
  

这不是我想要的。

这可能吗？是否有更简单的方法来表示任何类型的数字（包括潜在的BigDecimal）的NxM矩阵，或者我卡住了？

解决方案

 < T extends Number> T [] [] zeroMatrix（Class< ;? extends Number> int row，int col）{
 T [] [] matrix =（T [] []）java.lang.reflect.Array.newInstance行，列）; 
 T zero =（T）of.getConstructor（String.class）.newInstance（0）; 
 //不处理异常
 
 for（int i = 0; i< row; i ++）{
 for（int j = 0; j< col; 
矩阵[i] [j] =零; 
} 
} 
 
返回矩阵; 
} 
  

用法：

  BigInteger [] [] bigIntegerMatrix = zeroMatrix（BigInteger.class，3，3）; 
 Integer [] [] integerMatrix = zeroMatrix（Integer.class，3，3）; 
 Float [] [] floatMatrix = zeroMatrix（Float.class， 3，3）; 
 String [] [] error = zeroMatrix（String.class，3，3）; //< ---编译时错误
 System.out.println（Arrays.deepToString （bigIntegerMatrix））; 
 System.out.println（Arrays.deepToString（integerMatrix））; 
 System.out.println（Arrays.deepToString（floatMatrix））; 
 
 编辑 
 
 
 
一个通用矩阵：
  public static< T> T [] [] fillMatrix（Object fill，int row，int col）{
 T [ ] [] matrix =（T [] []）Array.newInstance（fill.getClass（），row，col）; （int j = 0; j  matrix [i]）的
 
（int i = 0; i } 
} 
 
返回矩阵; 
} 
 
 Integer [] [] zeroMatrix = fillMatrix（0，3，3）; //一个零填充的3x3矩阵
 String [] [] stringMatrix = fillMatrix（B，2，2）; //一个B填充的2x2矩阵
  
 
In an attempt to see if I can clean up some of my math code, mostly matrix stuff, I am trying to use some Java Generics. I have the following method:
private <T> T[][] zeroMatrix(int row, int col) {
    T[][] retVal = (T[][])new Object[row][col];
    for(int i = row; i < row; i++) {
        for(int j = col; j < col; j++) {
            retVal[i][j] = 0;
        }
    }
    return retVal;
}
The line retVal[i][j] = 0 is the one causing me headaches. The goal of the line is to initialize the array with the T representation of 0. I've attempted to do all sorts of things with it: (T is defined in the class as T extends Number)
retVal[i][j] = (T)0;
retVal[i][j] = new T(0);
The only thing that works is 
retVal[i][j] = (T)new Object(0);
Which is not what I want.

Is this possible? Is there an easier way to represent an NxM matrix of any type of Number(including potentially BigDecimal), or am I stuck?
解决方案
<T extends Number> T[][] zeroMatrix(Class<? extends Number> of, int row, int col) {
    T[][] matrix = (T[][]) java.lang.reflect.Array.newInstance(of, row, col);
    T zero = (T) of.getConstructor(String.class).newInstance("0");
    // not handling exception      

    for (int i = 0; i < row; i++) {
        for (int j = 0; j < col; 
            matrix[i][j] = zero;
        }
    }

    return matrix;
}
usage:
    BigInteger[][] bigIntegerMatrix = zeroMatrix(BigInteger.class, 3, 3);
    Integer[][] integerMatrix = zeroMatrix(Integer.class, 3, 3);
    Float[][] floatMatrix = zeroMatrix(Float.class, 3, 3);
    String[][] error = zeroMatrix(String.class, 3, 3); // <--- compile time error
    System.out.println(Arrays.deepToString(bigIntegerMatrix));
    System.out.println(Arrays.deepToString(integerMatrix));
    System.out.println(Arrays.deepToString(floatMatrix));
EDIT

a generic matrix:
public static <T> T[][] fillMatrix(Object fill, int row, int col) {
    T[][] matrix = (T[][]) Array.newInstance(fill.getClass(), row, col);

    for (int i = 0; i < row; i++) {
        for (int j = 0; j < col; j++) {
            matrix[i][j] = (T) fill;
        }
    }

    return matrix;
}    

Integer[][] zeroMatrix = fillMatrix(0, 3, 3); // a zero-filled 3x3 matrix
String[][] stringMatrix = fillMatrix("B", 2, 2); // a B-filled 2x2 matrix


                        
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