Transposing Values in Java 2D ArrayList

问题

Good evening all,

I'm trying to write a method that creates and returns a 2D array whose elements in each location are the same as the elements in the mirror image location of the parameter array. Unfortunately, no matter what pair of numbers I enter into the method call I get an "out of bounds" error in my compiler. Below is my program. Tell me where I've gone wrong! Thanks!

public static int[][] transpose(int [][] a) {
int r = a.length;
int c = a[r].length;
int [][] t = new int[c][r];
  for(int i = 0; i < r; ++i) {
     for(int j = 0; j < c; ++j) {
   t[j][i] = a[i][j];
   }
  }
return t;
 }
}

回答1:

Arrays in java are 0 based, change your assignment to c to :

int c = a[r - 1].length;

回答2:

@Suraj is correct, however you must assume the 2D array is rectangular, in which case it is sightly more efficient to change line 3 to:

int c = a[0].length;

@Kris answer text is correct however code sample is wrong line.

Note this error is a reproduction of a broken "answer" posted in "Yahoo Answers": http://answers.yahoo.com/question/index?qid=20080121204551AAn62RO

回答3:

Your problem lies in line two: a[r].length returns the number of columns, but arrays are indexed from 0. You should adjust accordingly:

int r = a.length - 1;

来源：https://stackoverflow.com/questions/5190419/transposing-values-in-java-2d-arraylist