for loops & for each loops?

Question

Below is a 'for each' loop. Under it is a few ways to write the same code but in 'for loop' version and as a 'while loop'. Are they correct? 



String[] cities = new String[ 10 ]; 
// missing code that inserts a String in each element of this array 

for ( String city : cities ) 
{ 
  if ( city.substring( 0, 1 ).equals( "C" ) ) 
    System.out.println( city ); 
} 

Can it be re-written as :


 String[] cities = new String[ 10 ]; 

// missing code that inserts a String in each element of this array 

for ( int i = 0 ; i < cities.length ; i++ ) 
{ 
  String city = cities[ i ]; 
  if ( city.substring( 0, 1 ).equals( "C" ) ) 
    System.out.println( city ); 
}  

and

String[] cities = new String[ 10 ]; 

// missing code that inserts a String in each element of this array 

for ( int i = 0 ; i < cities.length ; i++ ) 
{ 
  if ( cities[ i ].substring( 0, 1 ).equals( "C" ) ) 
    System.out.println( cities[ i ] ); 
} 

and
(while loop..)

String[] cities = new String[ 10 ]; 

// missing code that inserts a String in each element of this array 

int i = 0; 
while ( i < cities.length ) 
{ 
  String city = cities[ i ]; 

  if ( city.substring( 0, 1 ).equals( "C" ) ) 
    System.out.println( city ); 

  i++; 
}

Anonymous · Answer

You're making two invalid assumptions - that you'll know how many elements there are and that they can be enumerated.  If that's the case it wouldn't be written as a for each to begin with.  (In your second example, you're defining a string inside the loop - never do anything inside a loop that can be done outside it or that can be done a cheaper way.  Repeated code is expensive code.  if ( cities[i].substring( 0, 1 ).equals( "C" ) )  )

David · Answer

Probably quicker to compile and look for errors?

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for loops & for each loops?

2 Answers