External Interfaces/API

Assigning to a Java Array

You assign values to objects in a Java array in essentially the same way as you do in a MATLAB array. Although Java and MATLAB arrays are structured quite differently, you use the same command syntax to specify which elements you want to assign to. See How MATLAB Represents the Java Array for more information on Java and MATLAB array differences.

The following example deposits the value 300 in the dblArray element at row 3, column 2. In Java, this would be dblArray[2][1].

• dblArray(3,2) = java.lang.Double(300)
  dblArray =
  java.lang.Double[][]:
      [11]    [ 12]    [13]    [14]    [15]
      [21]    [ 22]    [23]    [24]    [25]
      [31]    [300]    [33]    [34]    [35]
      [41]    [ 42]    [43]    [44]    [45]
  

You use the same syntax to assign to an element in an object's data field. Continuing with the myMenuObj example shown in Accessing Elements of a Java Array, you assign to the third menu item in menuItemArray as follows.

• myMenuObj.menuItemArray(3) = java.lang.String('Save As...');
  

Using Single Subscript Indexing for Array Assignment

You can use a single-array subscript to index into a Java array structure that has more than one dimension. Refer to Using Single Subscript Indexing to Access Arrays for a description of this feature as used with Java arrays.

You can use single-subscript indexing to assign values to an array as well. The example below assigns a one-dimensional Java array, onedimArray, to a row of a two-dimensional Java array, dblArray. Start out by creating the one-dimensional array.

• onedimArray = javaArray('java.lang.Double', 5);
  for k = 1:5
      onedimArray(k) = java.lang.Double(100 * k);
      end
  

Since dblArray(3) refers to the 5-by-1 array displayed in the third row of dblArray, you can assign the entire, similarly dimensioned, 5-by-1 onedimArray to it.

• dblArray(3) = onedimArray
  dblArray =
  java.lang.Double[][]:
      [ 11]    [ 12]    [ 13]    [ 14]    [ 15]
      [ 21]    [ 22]    [ 23]    [ 24]    [ 25]
      [100]    [200]    [300]    [400]    [500]
      [ 41]    [ 42]    [ 43]    [ 44]    [ 45]
  

Assigning to a Linear Array

You can assign a value to every element of a multidimensional Java array by treating the array structure as if it were a single linear array. This entails replacing the single, numerical subscript with the MATLAB colon operator. If you start with the dblArray array, you can initialize the contents of every object in the two-dimensional array with the following statement.

• dblArray(:) = java.lang.Double(0)
  dblArray =
  java.lang.Double[][]:
      [0]    [0]    [0]    [0]    [0]
      [0]    [0]    [0]    [0]    [0]
      [0]    [0]    [0]    [0]    [0]
      [0]    [0]    [0]    [0]    [0]
  

Using the Colon Operator

You can use the MATLAB colon operator as you would when working with MATLAB arrays. The statements below assign given values to each of the four rows in the Java array, dblArray. Remember that each row actually represents a separate Java array in itself.

• dblArray(1,:) = java.lang.Double(125);
  dblArray(2,:) = java.lang.Double(250);
  dblArray(3,:) = java.lang.Double(375);
  dblArray(4,:) = java.lang.Double(500)
  dblArray =
  java.lang.Double[][]:
      [125]    [125]    [125]    [125]    [125]
      [250]    [250]    [250]    [250]    [250]
      [375]    [375]    [375]    [375]    [375]
      [500]    [500]    [500]    [500]    [500]
  

Assigning the Empty Matrix

When working with MATLAB arrays, you can assign the empty matrix, (i.e., the 0-by-0 array denoted by []) to an element of the array. For Java arrays, you can also assign [] to array elements. This stores the NULL value, rather than a 0-by-0 array, in the Java array element.

Subscripted Deletion

When you assign the empty matrix value to an entire row or column of a MATLAB array, you find that MATLAB actually removes the affected row or column from the array. In the example below, the empty matrix is assigned to all elements of the fourth column in the MATLAB matrix, matlabArray. Thus, the fourth column is completely eliminated from the matrix. This changes its dimensions from 4-by-5 to 4-by-4.

• matlabArray = [11 12 13 14 15; 21 22 23 24 25; ...
                 31 32 33 34 35; 41 42 43 44 45]
  matlabArray =
      11    12    13    14    15
      21    22    23    24    25
      31    32    33    34    35
      41    42    43    44    45
  
  matlabArray(:,4) = []
  matlabArray =
      11    12    13    15
      21    22    23    25
      31    32    33    35
      41    42    43    45
  

You can assign the empty matrix to a Java array, but the effect will be different. The next example shows that, when the same operation is performed on a Java array, the structure is not collapsed; it maintains its 4-by-5 dimensions.

• dblArray(:,4) = []
  dblArray =
  java.lang.Double[][]:
      [125]    [125]    [125]     []    [125]
      [250]    [250]    [250]     []    [250]
      [375]    [375]    [375]     []    [375]
      [500]    [500]    [500]     []    [500]
  

The dblArray data structure s actually an array of five-element arrays of java.lang.Double objects. The empty array assignment placed the NULL value in the fourth element of each of the lower level arrays.

Accessing Elements of a Java Array

Concatenating Java Arrays