How to convert string to long in Java is one of those frequently asked
questions by beginner who has started learning Java programming language and
not aware of how to convert from one data type to another. Converting String to
long is similar to converting String to Integer in Java, in-fact if you know how
to convert String to Integer than you can convert String to Long by following same procedure. Though you need
to remember few things while dealing with long and String first of all long is
primitive type which is wrapped by Long wrapper
class and String is an Object
in Java backed by character array. Before Java 5 you need to take an extra
step to convert Long object into long primitive
but after introduction of autoboxing
and unboxing in Java 5, Java language will perform that conversion for you.
This article is in continuation of our previous conversion tutorial like how to
convert
String to Double in Java or how
to convert String to Enum in Java. In this Java tutorial we will learn 3
different ways to convert String to long by code example and we will also analyze
pros and cons of each approach.
How to convert String to long in Java
Here are 3 different ways to convert an String to long primitive value in
Java:
1) Using Long.valueOf() method
2) Using Long.parseLong() method
3) Using java.lang.Long constructor
4) Using Long decode() method
String
to long - Long.valueOf
Long.valueOf() is staticfactory method from java.lang.Long class which accepts an String
argument and returns an equivalent long primitive
value. Long.valueOf() will throw NumberFormatException if String
is not convertible into long due to any reason like String contains non numeric
value, numeric value of String is beyond MAX and MIN value of Long etc. Though
negative sign can be included to denote negative long value as first character.
Main advantage of valueOf() is that its an static factory
method and can cache frequently used long value, since long is an immutable
object its safe to reuse cached long values. valueOf() is also an
overloaded
method which accepts radix as second argument to convert
hexadecimal or octal String to long. Here is an example of converting String to long value using valueOf method in
Java:
long decimalNumber = Long.valueOf("55555");
long octalNumber = Long.valueOf("55555", 8);
long hexNumber = Long.valueOf("5555", 16);
As per caching JDK's Long.valueOf() method
caches values upto -128 to 127 and returns same Long object which will return
true if compared with equality
operator "==". you can also look code of valueOf() method on java.lang.Long class to
verify it.
String
to long - Long.parseLong
Long.parseLong() is another static
method from java.lang.Long class which converts String into
long value. parseLong() also throws java.lang.NumberFormatException if
provided String value is not convertible into long and also provides addition
overloaded method which accepts radix to convert octal and hexadecimal long
values in String
format. Most of the String to long conversion uses parseLong for conversion
part, in fact Long.valueOf() also calls parseLong method to
convert long to String. parseLong() also accepts negative sign as
first character in string input. Though "l" and "L" values are
not permitted inside String input and throw NumberFormatException.
long negativeLong = Long.parseLong("-1024"); //represent
negative long value
long incorrectLong = Long.parseLong("-1024L"); // "L"
is not permitted result in NumberFormatException
Long.decode()
and Long Constructor
Other two methods using a java.lang.Long constructor
which accepts String and Long.decode() also work in similar fashion.
They also throw NumberFormatException if String is not
convertible into long. Long.decode() is good in terms it accepts "#" as
indication of hexadecimal long values. It also accept "0" for octal
long numbers, "0x" and "0X" for hexadecimal long numbers. Here
is an example of using Long.decode() method to convert hexadecimal
long String value into long primitive number:
see code example section for more examples of decode() method of
Long class.
Code
Example - String to long conversion in Java
Here is complete code example of all four ways to convert String to long
in Java discussed in this Java tutorial.
/**
* Java program to convert String to long in Java. In this program
we will see 4 examples
* to convert String to long primitive in Java.
* @author Javin Paul
*/
public class
StringToLong {
public static void
main(String args[]) {
String strLong = "2323232";
//Convert String to
long using Long.valueOf(),better because
//it can cache
frequently used long values
long
number = Long.valueOf(strLong);
System.out.println("String to long conversion using valueOf :"
+ number);
//Convert String to
long in Java using java.lang.Long object
strLong ="4444444444444444444";
Long numberObject = new Long(strLong);
number = numberObject;
//auto boxing will take care of long to Long
conversion
System.out.println("String to long conversion example using Long object:
" + number);
//Convert String to
long with Long.parseLong method in Java
strLong="999999999999999999";
Long parsedLong = Long.parseLong(strLong) ;
number = parsedLong;
//auto-boxing will convert Long object to
primitive long
System.out.println("String to long conversion using parseLong() method:
" + number);
//Convert String to
long using Long.decode() method in Java
strLong ="-1023454";
number = Long.decode(strLong);
System.out.println("String to long conversion using decode() method:
" + number);
//String to long in
hexadecimal format
strLong ="0xFFFF";
number = Long.decode(strLong);
System.out.println("String to long example in hex format decode() method:
" + number);
//String to long in
octal format
strLong ="0777";
number = Long.decode(strLong);
System.out.println("String to long example in octal format decode()
method: " + number);
}
}
Output:
String to long conversion
using valueOf :2323232
String to long conversion
example using Long object: 4444444444444444444
String to long conversion
using parseLong() method: 999999999999999999
String to long conversion
using decode() method: -1023454
String to long example in hex
format decode() method: 65535
String to long example in
octal format decode() method: 511
That’s all on How to convert String to long in Java. We have seen
four ways to change String values to long e.g. Long.valueOf(), Long.parseLong() and Long.decode() method
along with classic constructor approach for converting String to long in Java.
I personally prefer Long.valueOf() most of the time and
Long.parseLong() in rest of time to convert String to long.
Other Java programming tutorials for beginners from Javarevisited
Blog
Source:http://javarevisited.blogspot.com/2012/12/how-to-convert-string-to-long-in-java-4-examples.html
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