Multi-dimension arrays

[Mike Lipay]

If I have a multi-dimensional array that I want to loop through, how do I setup the for loop? I thought this would work, but it doesn't compile.

private Object[][] serviceTable = {
	{ 97300, "1/26/2009", "McElhinney's Service", 4798, "Check alternator and oil pressure", "Battery, Alternator, Serpentine Belt, Oil Pressure Sensor", 707.68},
	{ 0, "3/20/2008", "McElhinney's Service", 11112, "Replace engine", "Motor, cables, fluids", 4534.61}
};


for (Object r : serviceTable)
	for (Object c: serviceTable[r])
		System.out.println(serviceTable[r][c]);

I know I can do it with a regular

for (r = 0; r < 2; r++)...

but I was wondering if there was a way to do it as above.

[Peter Taucher]

On the first hierarchy you loop over arrays of objects (not object). Take a look:

Object[][] serviceTable = {
    { 97300, "1/26/2009", "McElhinney's Service", 4798, "Check alternator and oil pressure", "Battery, Alternator, Serpentine Belt, Oil Pressure Sensor", 707.68 },
    { 0, "3/20/2008", "McElhinney's Service", 11112, "Replace engine", "Motor, cables, fluids", 4534.61 }
};

for ( Object[] r : serviceTable )
    for ( Object c : r )
        System.out.println( c );

for ( int r = 0; r < serviceTable.length; r++ )
    for ( int c = 0; c < serviceTable[r].length; c++ )
        System.out.println( r + ", " + c + " -> " + serviceTable[r][c] );

[Seetharaman Venkatasamy]

better to say *array of arrays* insteadof multidimensional . your for loop declaration is wrong .

[Peter Taucher]

Okay, let's say 'array of arrays' ... but because arrays are objects too (special ones of corse), erm ... nevermind ; - )

[Mike Lipay]

Peter Taucher wrote:On the first hierarchy you loop over arrays of objects (not object). Take a look:

Object[][] serviceTable = {
    { 97300, "1/26/2009", "McElhinney's Service", 4798, "Check alternator and oil pressure", "Battery, Alternator, Serpentine Belt, Oil Pressure Sensor", 707.68 },
    { 0, "3/20/2008", "McElhinney's Service", 11112, "Replace engine", "Motor, cables, fluids", 4534.61 }
};

for ( Object[] r : serviceTable )
    for ( Object c : r )
        System.out.println( c );

Ok, I get it. In the outer loop "r" actually becomes an array for the row, then in the inner loop the "c" becomes the individual cell within the row. Out of curiosity, if there are three dimensions to the array, would this be the code:

for (Object[] x : serviceTable)
   for (Object[] y : x)
      for (Object z : y)
         System.out.println (z);

[Mike Lipay]

Seetharaman Venkatasamy wrote:better to say *array of arrays* insteadof multidimensional . your for loop declaration is wrong .

Sorry, multi-dimensional is how I've always seen nested arrays referred to. I'm guessing "array of arrays" is a java term. I'll try to remember this in the future.

[Peter Taucher]

Mike Lipay wrote:Ok, I get it. In the outer loop "r" actually becomes an array for the row, then in the inner loop the "c" becomes the individual cell within the row. Out of curiosity, if there are three dimensions to the array, would this be the code:

for (Object[] x : serviceTable)
   for (Object[] y : x)
      for (Object z : y)
         System.out.println (z);

Not exactly. I'd say it has to look like this:

for (Object[][] x : serviceTable)
   for (Object[] y : x)
      for (Object z : y)
         System.out.println (z);

[Campbell Ritchie]

Java arrays are not multi-dimensional but arrays of arrays. If they were multi-dimensional, the individual members would have to be the same size, which is not the case in Java. Arrays of arrays may also allow different placement of the data in memory, re-assignment of members, etc.

[Lalit Mehra]

Peter Taucher wrote:

Mike Lipay wrote:Ok, I get it. In the outer loop "r" actually becomes an array for the row, then in the inner loop the "c" becomes the individual cell within the row. Out of curiosity, if there are three dimensions to the array, would this be the code:

for (Object[] x : serviceTable)
   for (Object[] y : x)
      for (Object z : y)
         System.out.println (z);

Not exactly. I'd say it has to look like this:

for (Object[][] x : serviceTable)
   for (Object[] y : x)
      for (Object z : y)
         System.out.println (z);

with the multidimensionality of the array of arrays ... i guess i am quoting write

the outermost for loop argument contains the most significant array of the arrays and with each inner loop argument containing the less significant one than the previous one

Lucky