Java - Convert String to long
To convert a String to long in Java, we can use:
Long.parseLong()
- static long parseLong(String s): Parses the string argument as a signed decimal long.
- static long parseLong(String s, int radix): Parses the string argument as a signed long in the radix specified by the second argument.
long l1 = Long.parseLong("999");
System.out.println(l1); // 999
long l2 = Long.parseLong("-FF", 16);
System.out.println(l2); // -255
long l3 = Long.parseLong("01010101", 2);
System.out.println(l3); // 85
We also can use Long.parseUnsignedLong(...) to make sure the long is > 0.
Long.valueOf()
The difference between valueOf(...) and parseLong(...) is valueOf(...) will return a Long (wrapper class) instead of primitive long.
- static Long valueOf(String s): Returns a Long object holding the value of the specified String.
- static Long valueOf(String s, int radix): Returns a Long object holding the value extracted from the specified String when parsed with the radix given by the second argument.
long l1 = Long.valueOf("888");
System.out.println(l1); // 101010101
long l2 = Long.valueOf("-FF", 16);
System.out.println(l2); // -255
long l3 = Long.valueOf("01010101", 2);
System.out.println(l3); // 85
As you can see, implicit casting automatically unbox Long into long.
Deprecated: Long‘s Constructor
Long(String s) is deprecated.
It is rarely appropriate to use this constructor. Use parseLong(String) to convert a string to a long primitive, or use valueOf(String) to convert a string to a Long object.
long l1 = new Long("123");
System.out.println(l1); // 123
long l2 = new Long("-0x8F"); // NumberFormatException
System.out.println(l2);
Long.decode()
static Long decode(String nm): Decodes a String into a Long.
long l1 = Long.decode("321");
System.out.println(l1); // 321
long l2 = Long.decode("-0x88"); // hex
System.out.println(l2); // -136
long l3 = Long.decode("#F3F3F3"); // hex
System.out.println(l3); // 15987699
long l4 = Long.decode("066"); // octal
System.out.println(l4); // 54
DecimalFormat.parse()
parse(String source) throws ParseException: Parses text from the beginning of the given string to produce a number. The method may not use the entire text of the given string.
import java.text.DecimalFormat; import java.text.ParseException;
DecimalFormat decimalFormat = new DecimalFormat();
try {
long l = decimalFormat.parse("54321").longValue();
System.out.println(l); // 54321
} catch (ParseException e) {
System.out.println(e.getMessage());
}
Since parse() method returns instance of Number, we need to call longValue() to get the long primitive value from it. The Number also has intValue() to get int primitive value, doubleValue() for double, etc.
And similar to Convert String to int, we also can use external libraries like Apache Commons NumberUtils, Spring's NumberUtils, and Google's Guava primitive Longs.
Apache Commons NumberUtils
Methods:
- static long toLong(String str): Convert a String to a long, returning zero if the conversion fails.
- static long toLong(String str, long defaultValue): Convert a String to a long, returning a default value if the conversion fails.
- static Long createLong(String str): Convert a String to a Long; since 3.1 it handles hex (0Xhhhh) and octal (0ddd) notations.
import org.springframework.util.NumberUtils;
long l1 = NumberUtils.toLong("365");
System.out.println(l1); // 365
long l2 = NumberUtils.toLong(null);
System.out.println(l2); // 0
long l3 = NumberUtils.toLong("365", 0);
System.out.println(l3); // 365
long l4 = NumberUtils.toLong("xyz", -1);
System.out.println(l4); // -1
long l5 = NumberUtils.toLong("", -1);
System.out.println(l5); // -1
long l6 = NumberUtils.createLong("365");
System.out.println(l6); // 365
long l7 = NumberUtils.createLong("-0xFF88");
System.out.println(l7); // -65416
Spring NumberUtils
Similar like in Converting String to int, we can use Spring's NumberUtils to parse String to number (in this case long).
import org.springframework.util.NumberUtils;
long i1 = NumberUtils.parseNumber("512", Long.class);
System.out.println(i1); // 512
long i2 = NumberUtils.parseNumber("#F120", Long.class);
System.out.println(i2); // 61728
Google Guava Longs.tryParse()
The conversion also can be done using Guava’s Longs.tryParse().
Methods:
- static Long tryParse(String string): Parses the specified string as a signed decimal long value.
- static Long tryParse(String string, int radix): Parses the specified string as a signed long value using the specified radix.
import com.google.common.primitives.Longs;
long l1 = Longs.tryParse("5123456789012346");
System.out.println(l1); // 5123456789012346
long l2 = Longs.tryParse("-18F1", 16);
System.out.println(l2); // -6385
long l3 = Longs.tryParse("111111111", 2);
System.out.println(l3); // 511
Also check on How to Handle NumberFormatException in Java
Desson AriawanProgrammer