Overriding Equals

1) equals method implementation

public boolean equals(Object o){
if((o instaceof x) && o.value() == this.value())
 return true;
else 
return false;
}

//Consideration of two different classes as equal is bad.

- if you override equals() then it is better to override hashcode()


2) collections

3) Collection - base class for list, set and queue (except map)

4) Collections - class with Static helper methods.

5) ArrayList - Non-synchronized list having get(int index) getIndex(Object o) method, easier for iteration, faster than Vector.

List<generic> = new ArrayList();

add() to add a value;

remove();

contains();

- AutoBoxing wraps primitive types to their corresponding objects.

- Collection/Array should be sorted before searching.

6) converting arrays to lists and lists to arrays

1) toArray();

2) Arrays.toList();



7) Sets are used when you dont want any duplicate values in your collection.

Set s = new HashSet();

add() , remove(), contain() ;

- To use a treeset the objects should be mutually comparable.

- Always override equals and hashcode methods.

8) Navigation through TreeSets and TreeMaps.

 NavigableSet and NavigableMap.

NavigableSet methods - lower(), higher(), ceiliing() and floor() methods introduced as of java6

 NavigationMap methods - lowerKey(), higherKey(), ceilingKey() and floorKey();

 lower() - gives the element that is lower than specified;

 higher() - gives element that is higher than specified.

ceil() - gives element that is equal to or higher than specified.

 floor() - gives element that is equal to or higher than specified.

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