I think my answer can be more understandable:
There are two differences between & and &&.
If they use as logical AND
& and && can be logical AND, when the & or && left and right expression result all is true, the whole operation result can be true.
when & and && as logical AND, there is a difference:
when use && as logical AND, if the left expression result is false, the right expression will not execute.
Take the example :
String str = null;
if(str!=null && !str.equals("")){ // the right expression will not execute
}
If using &:
String str = null;
if(str!=null & !str.equals("")){ // the right expression will execute, and throw the NullPointerException
}
An other more example:
int x = 0;
int y = 2;
if(x==0 & ++y>2){
System.out.print(“y=”+y); // print is: y=3
}
int x = 0;
int y = 2;
if(x==0 && ++y>2){
System.out.print(“y=”+y); // print is: y=2
}
& can be used as bit operator
& can be used as Bitwise AND operator, && can not.
The bitwise AND " &" operator produces 1 if and only if both of the bits in its operands are 1. However, if both of the bits are 0 or both of the bits are different then this operator produces 0. To be more precise bitwise AND " &" operator returns 1 if any of the two bits is 1 and it returns 0 if any of the bits is 0.
From the wiki page:
http://www.roseindia.net/java/master-java/java-bitwise-and.shtml