Long class forms the primitive type long, which can represent an integer number of 32 bits (2^32). A very common procedure in Java programming is the conversion of String to Long.
As you can expect, in this example we are going to show how to convert a string to long in every possible way.
1. Syntax of the convert operations
First of all, in order to convert a string to long, we can simply create a Long object by setting the specified string to its constructor. Otherwise you can use different operations, as you can see below:
public static Long valueOf(String s, int radix): returns aLongobject that includes the long value of the given strings, when parsed with the specified radix.public static Long valueOf(String s): it is like the above function but there is no need of the second argument, because the radix is decimal by default.public static long parseLong(String s,int radix): returns a signed long that is interpreted by the specified string when parsed by the given radix.public static long parseLong(String s): returns a new long that is represented by the specified strings. The radix is set to 10 (default value).public static Long decode(String nm): returns aLongthat keeps a long value of the specifiedString. In this method in order to define the radix of the long number, we should set a specific portion in front of the string. More specifically this operation accepts decimal, hexadecimal, and octal signed numbers so the specified radix for hexadecimal is0xor0Xor#and for octal is simply a leading zero.
It is worth to mention that if the string cannot be parsed, all the above operations throw a NumberFormatException.
2. Example of String to Long conversion
Create a new java file with the name StringToLongClass and paste the following code.
StringToLongClass.java:
package com.javacodegeeks.basics.stringtolong;
public class StringToLongClass {
public static void main(String[] args) {
String str = "1234567890123";
Long longNum = new Long(str);
System.out.println("Use of constructor: longNum = "+longNum.longValue());
long long1 = Long.parseLong(str);
System.out.println("Use of parseLong: long1 = "+long1);
long l1 = Long.valueOf(str).longValue();
System.out.println("Use of valueOf: l1 = "+l1);
// with a specified radix
long long2 = Long.parseLong("-AAAAAAAA", 16);
System.out.println("Use of parseLong with 16 radix: long2 = "+long2);
// returns a Long object. radix=36 for ISO basic Latin alphabet
Long l2 = Long.valueOf("JCG", 36);
System.out.println("Use of valueOf with 36 radix: l2 = "+l2);
// for octal format use 0
long decLong1 = Long.decode("0776");
System.out.println("Use of decode with octal format: decLong1 = "+decLong1);
// for hex format use 0x or 0X or #
long decLong2 = Long.decode("0xFFFFFFFFE");
System.out.println("Use of decode with hex format: decLong2 = "+decLong2);
// exception conditions
try {
long long3 = Long.parseLong("FFC", 8);
} catch (NumberFormatException e) {
System.err.println("NumberFormatException in parseLong, "+ e.getMessage());
}
try {
Long l3 = Long.valueOf("hi");
} catch (NumberFormatException e) {
System.err.println("NumberFormatException in valueOf, "+ e.getMessage());
}
try {
Long decLong3 = Long.decode("#FFG");
} catch (NumberFormatException e) {
System.err.println("NumberFormatException in decode, "+ e.getMessage());
}
}
}
As you can see in the code above, we call parseLong() and valueOf() methods with the default decimal radix as well as with the use of a specified radix and a sign (+/-). For instance if the indicated radix is set to 16, a hexadecimal number is defined. Also notice that longValue() is used in the returned value of valueOf() operation, in order to transform the Long object to long data type. Now have a look to decode() operation. As we mentioned above, the leading zero indicates an octal number and 0x specifies a hexadecimal number.
Of course, we couldn’t disregard the exception conditions for the used methods. long3 throws an exception because the specified string can not be parsed as an octal number. In parallel l3 throws NumberFormatException too, because we just declare a string value without specifying the appropriate radix. Finally, decLong3 throws the same exception because "FFG" doesn’t represent a hexadecimal number.
Below, you can see the output of the execution.
Output:
Use of constructor: longNum = 1234567890123
Use of parseLong: long1 = 1234567890123
Use of valueOf: l1 = 1234567890123
Use of parseLong with 16 radix: long2 = -2863311530
Use of valueOf with 36 radix: l2 = 25072
Use of decode with octal format: decLong1 = 510
Use of decode with hex format: decLong2 = 68719476734
NumberFormatException in parseLong, For input string: "FFC"
NumberFormatException in valueOf, For input string: "hi"
NumberFormatException in decode, For input string: "FFG"
Download the source code
This was an example of string to long in Java. Download the source code of this example: StringToLongExample.zip
