valueOf() is a static method of the Long wrapper class in Java. This post will discuss the valueOf() method in detail.
Long class has provided three overloaded implementations of the valueOf() method –
- public static Long valueOf(long l)
- public static Long valueOf(String s)
- public static Long valueOf(String s, int radix)
Let’s look at each of them one by one.
public static Long valueOf(long l)
- What does it do? It will take a long primitive value as an argument and create an instance of the Long class representing that value.
- What does it return? It will return a Long instance representing the value passed in the argument.
Note: valueOf() is the preferred way of creating the objects of the Long class because it provides better space and time performance over the normal constructors.
Code Example
public class Codekru {
public static void main(String[] args) {
long longValue = 134242342;
Long longInstance = Long.valueOf(longValue);
System.out.println("Long instance value: " + longInstance);
}
}
Output –
Long instance value: 134242342
Time complexity of Long valueOf(long l) method
The time complexity of the valueOf(long l) method is O(1).
public static Long valueOf(String s)
It will take a string as an argument and convert it into a Long instance.
Note: We can only pass a string containing decimal characters with an optional positive or negative character at the beginning. If we pass any other character, it will throw a NumberFormatException.
Code Example
public class Codekru {
public static void main(String[] args) {
String str1 = "1234";
String str2 = "+1234";
String str3 = "-1234";
Long longInstance1 = Long.valueOf(str1);
Long longInstance2 = Long.valueOf(str2);
Long longInstance3 = Long.valueOf(str3);
System.out.println("Long instance representing str1: " + longInstance1);
System.out.println("Long instance representing str2: " + longInstance2);
System.out.println("Long instance representing str3: " + longInstance3);
}
}
Output –
Long instance representing str1: 1234
Long instance representing str2: 1234
Long instance representing str3: -1234
What if we pass other characters and not just decimal characters?
valueOf() method will throw a NumberFormatException as illustrated below.
public class Codekru {
public static void main(String[] args) {
String str = "twenty";
Long longInstance = Long.valueOf(str);
System.out.println("Long instance representing str1: " + longInstance);
}
}
Output –
Exception in thread "main" java.lang.NumberFormatException: For input string: "twenty"
at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:68)
at java.base/java.lang.Long.parseLong(Long.java:707)
at java.base/java.lang.Long.valueOf(Long.java:1159)What if we pass null as an argument?
It will also throw a NumberFormatException
public class Codekru {
public static void main(String[] args) {
Long longInstance = Long.valueOf(null);
System.out.println("Long instance value: " + longInstance);
}
}
Output –
Exception in thread "main" java.lang.NumberFormatException: null
at java.base/java.lang.Long.parseLong(Long.java:670)
at java.base/java.lang.Long.valueOf(Long.java:1159)Internal implementation of the valueOf(String s) method
public static Long valueOf(String s) throws NumberFormatException{
return Long.valueOf(parseLong(s, 10));
}
valueOf(String s) internally uses –
- parseLong() method to first parse the string.
- and then uses the valueOf(long l) method to create the Long instance.
Time complexity of the valueOf(String s) method
parseLong() method has a time complexity of O(n) and valueOf(long l) has O(1) time complexity. So, the time complexity of valueOf(String s) is O(n), where n is the length of the string.
public static Long valueOf(String s, int radix)
It will also convert a string into a Long instance but according to the radix passed as the second argument.
What role will radix play while parsing the string?
This is similar to how we convert a binary number to a decimal number using base 2.
Let’s show you one sample conversion of number 220 using radix 4.
So, Long.valueOf(“220”,4) will return a Long instance with value 40.
public class Codekru {
public static void main(String[] args) {
Long longInstance = Long.valueOf("220", 4);
System.out.println("Long instance value: " + longInstance);
}
}
Output –
Long instance representing str1: 40
Some important points
- We can also use other than decimal characters, provided that the radix supports it. Eg. We can pass A, B, C, D, E and F with radix 16.
public class Codekru {
public static void main(String[] args) {
Long longInstance = Long.valueOf("220F", 16);
System.out.println("Long instance value: " + longInstance);
}
}
Output –
Long instance value: 8719
- The radix can only be between 2 and 36 ( inclusive ). If it is less than 2 or greater than 36, it will throw a NumberFormatException.
public class Codekru {
public static void main(String[] args) {
Long longInstance = Long.valueOf("220F", 37);
System.out.println("Long instance value: " + longInstance);
}
}
Output –
Exception in thread "main" java.lang.NumberFormatException: radix 37 greater than Character.MAX_RADIX
at java.base/java.lang.Long.parseLong(Long.java:678)
at java.base/java.lang.Long.valueOf(Long.java:1132)Please visit this link to learn more about the Long wrapper class of java and its other functions or methods.
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