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int values that are greater than or equal to 0 and less than the length of the array. Remember that computer scientists always count starting at zero, not one!IndexOutOfBoundsException to be thrown.myArray[i] = aValue; someValue = myArray[j]; More information on loops can be found at the Java Resources web site page on loops .
The main technique used to process arrays is the
for loop . A
for loop is a way of processing each element of the array in a sequential manner.
Here is a typical
for loop:
// Sum the number of elements in an array of ints, myArray.
int sum = 0; // initialize the sumfor(int idx=0; idx<myArray.length; idx++) { //start idx @ 0; end idx at length-1;
//increment idx every time the loop is processed.sum += myArray[idx]; // add the idx'th element of myArray to the sum}
There are a number of things going on in the above
for loop:
idx is being declared and initialized to zero.
idx is visible only within the
for loop body (between the curly braces).idx is being tested in a "termination condition", in this case,
idx is compared to the length of the list. If the termination condition evaluates to
false , the loop will immediately terminate.idx 's element in the array is being added to the running sum.idx is being incremented.One can traverse an array in any direction one wishes:
// Sum the number of elements in an array of ints, myArray.
int sum = 0; // initialize the sumfor(int idx=myArray.length-1; 0<=idx; idx--) { //start idx @ length-1; end idx at 0;
//decrement idx every time the loop is processed.sum += myArray[idx]; // add the idx'th element of myArray to the sum}
The above loop sums the list just as well as the first example, but it does it from back to front. Note however, that we had to be a little careful on how we initialized the index and how we set up the termination condition.
Here's a little more complicated loop:
// Find the index of the smallest element in an array of ints, myArray.
int minIdx = 0; // initialize the index. Must be declared outside the loop.if(0==myArray.length) throw new NoSuchElementException("Empty array!"); //No good if array
//is empty!else {
for(minIdx = 0, int j = 1; j<myArray.length; j++) { //start minIdx @ 0, start index @ 1;
//end index at length-1; increment// index every time the loop is
//processed.if(myArray[minIdx]>myArray[j])minIdx = j; // found new minimum
}}
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