methods - Why should we use a List of a particular type in Java -

i going through lesson in java, , lesson covers passing arraylist object through static method. in first static method, see arraylist had declared arraylist, , name it. first static method displays of elements in array. second static method changes elements of arraylist. when declaring arraylist in method, must declared arraylist<integer> modification purposes. why way, , why make difference? thank willing shed light on this.

import java.util.arraylist;  public class chap11part5 {     public static void main(string[] args)     {          arraylist<integer> numbers = new arraylist<integer>();          //for-loop create elements arraylist         (int = 1; < 11; ++i)             numbers.add(i);          display(numbers); //display elements         change(numbers, 5); //change elements (see "change" method)         display(numbers); //display new results       }      //loop display elements of arraylist     static void display(arraylist arr) {         for(int = 0; < arr.size(); ++i)             system.out.print(arr.get(i) + " ");         system.out.println();     }     //loop change elements of arraylist     static void change(arraylist<integer> arr, int amount) {         int value;         for(int = 0; < arr.size(); ++i) {             value = arr.get(i);             arr.set(i, value + amount);         }     }  } 

the <> syntax called generics - allows limit type of elements collection holds, , refer them type. it's not required, it's more convenient.

for instance, write second method without generics specified, you'd have handle casting yourself:

static void change(arraylist arr, int amount) {     int value;     for(int = 0; < arr.size(); ++i) {         value = (integer) arr.get(i); // explicit casting here. yuck!         arr.set(i, value + amount);     } }