The beauty of using Generics in Java

The beauty of using Generics in Java

by | Mar 16, 2022 | code fussion

Our pride as senior developers is succinct and accurate code, an algorithm that works and is not redundant. I used to adore complex-looking code back when I was first learning to code. But I couldn’t make out what was going on.

checkedSortedMap​(SortedMap<K,​V> m, Class<K> keyType, Class<V> valueType)

Writing Generic Algorithms

Some algorithms can be used for a variety of tasks. For example, suppose you wish to do a binary search across a large range of datatypes. You’d have to repeat the code as many times as the implementation required without generics.

public int runBinarySearchRecursively(
  int[] sortedArray, int key, int low, int high) {
    int middle = low  + ((high - low) / 2);
        
    if (high < low) {
        return -1;
    }

    if (key == sortedArray[middle]) {
        return middle;
    } else if (key < sortedArray[middle]) {
        return runBinarySearchRecursively(
          sortedArray, key, low, middle - 1);
    } else {
        return runBinarySearchRecursively(
          sortedArray, key, middle + 1, high);
    }
}

This code will only work with a list of sorted integers… what if you wanted it to also work with floating points or even variable characters?

public class BinarySearch<T extends Comparable<T>> {
 
 
 
        public int search(Comparable<T> v) {
            int low = 0;
            int high = a.length - 1;
             
            while (low <= high) {
                int mid = (low + high) / 2;
                T midVal = a[mid];
                int result = v.compareTo(midVal);
                if (result < 0) {
                    high = mid - 1;
                } else if (result > 0) {
                    low = mid + 1;
                } else {
                    return mid;
                }
            }
            return -1;
        }

Stronger type checks at compile time.

A Java compiler applies strong type checking to generic code and issues errors if the code violates type safety. Fixing compile-time errors is easier than fixing runtime errors, which can be difficult to find.

Limination of casts.

//Without Generics
List list = new ArrayList();
list.add("hello");
String s = (String) list.get(0);

//When re-written to use generics, the code does not require casting:
List<String> list = new ArrayList<String>();
list.add("hello");
String s = list.get(0);   // no cast

In conclusion

When compiling a class or interface that extends a parameterized class or implements a parameterized interface, the compiler may need to create a synthetic method, which is called a bridge method, as part of the type erasure process. You normally don’t need to worry about bridge methods, but you might be puzzled if one appears in a stack trace.

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