why use generic in real life in programming

object[] objectArray = new string[] { "string 1", "string 2" };

public class ObjectContainer {
    private Object obj;

    /**
     * @return the obj
     */
    public Object getObj() {
        return obj;
    }

    /**
     * @param obj the obj to set
     */
    public void setObj(Object obj) {
        this.obj = obj;
    }

}

List<String> list = new ArrayList<String>();
list.add("hello");
String s = list.get(0);   // no cast

List list = new ArrayList();
list.add("hello");
String s = (String) list.get(0);