Both of the following do the same

Option1

Given the following String somestring; void dosomething(){}

Consider the following code

if (somestring!=null&&!"".equals(somestring))
{
	//if the string is not empty
	dosomething();
}

Option 2

Create a function as follows

boolean isValid(String somestring)
{
	if (somestring == null) 
	{
		//the string is null. so it is not a valid string
		return false;
	}
	
	//the string is not null
	
	//eliminate empty characters at both ends
	String newstring = somestring.trim();
	if (newstring.equals(""))
	{
		//the string is an empty string
		//an empty string is (not) valid
		return false;
	}
	
	//it is a valid string because it is not null, it is not empty
	return true; 
}

Then you can do

if (isValid(somestring))
{
	//if the string is not empty
	dosomething();
}

To contrast

if (somestring!=null&&!"".equals(somestring))
{
	//if the string is not empty
	dosomething();
}

if (isValid(somestring))
{
	//if the string is not empty
	dosomething();
}