More On Arrays

Review of Arrays

• Declaring
  
• double[] testmark;
• Assign Space
• testMark = new double[5]
• Use Elements in Array
• testMark[3] = 720;

• an array is a table of values stored in memory
• the array name (testMark) is a reference to the array, just like object references
• to refer the ith member of the array
• testMark[i]
• Very Important
• array indices start at zero, not one.
• use testMark.length
• length is the keyword to get the length of the array
• arrays are objects
• they should be treated as such
• because we can change the elements of an array and because arrays are objects we have to treat them as mutable objects
  
• deep copy, defensive copy
• look again at testMark

double[]copyMarks; // create a copy of testMarks
copyMarks = testmarks //BAD!!!

• both references (copyMarks and testMarks) point to the same thing
• remember this also happens with object references
• how do we create a copy of an array?
1. allocate new space
2. individually copy elements

testMark = new double[5]
int i;
for (i=0, i < testMark.length, i++)
{
copyMark[i] = testMark[i];
}

• Summary
• Arrays are mutable objects which means Defensive copying
• copy on object containing an array
• deep copy
• so i do deep copy test mark
• testMark == copyMark
• this is not the same reference
• unfortunately equals() does not exist for arrays
• there exist java utilities for array equals
• java.util.arrays
• equals
• fill
• sort
  

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