In Java, valueOf() is a method that belongs to the String class. The valueOf() method is used to convert different types of data into a String object. There are several overloaded versions of the valueOf() method in Java that can convert different types of data into a String. Here is an example of the basic valueOf() method:
String s = String.valueOf(123);
This code converts the int value 123 into a String object and assigns it to the variable s. The resulting String object will contain the characters “123”. Here’s another example that converts a double value into a String:
double d = 3.14159; String s = String.valueOf(d);
In this example, the double value 3.14159 is converted into a String object and assigned to the variable s.
The valueOf() method can also be used to convert other types of data, such as boolean, char, and Object types, into String objects.
Internal implementation:
The valueOf() method in Java internally makes use of the StringBuilder class to create a String object. The StringBuilder class is used to efficiently construct a String by appending characters to it.
When you call the valueOf() method with a primitive data type or a character array, it creates a new StringBuilder object and appends the input data to it using the appropriate method, such as append(int) or append(char[]). Once the data has been appended, the toString() method of the StringBuilder class is called to convert the StringBuilder object to a String object.
Here’s an example of the internal implementation of the valueOf() method for converting an int value to a String:
public static String valueOf(int i) {
char[] buf = new char[11];
int pos = 10;
boolean negative = (i < 0);
if (!negative) {
i = -i;
}
while (i <= -10) {
buf[pos--] = (char) ('0' - (i % 10));
i /= 10;
}
buf[pos] = (char) ('0' - i);
if (negative) {
buf[--pos] = '-';
}
return new String(buf, pos, (11 - pos));
}
This code creates a char array of length 11, since the largest possible int value has 10 digits plus an optional negative sign. It then determines whether the input int is negative and, if so, makes it positive and sets a flag to indicate that the output String should be negative. It then extracts each digit of the input int using integer division and modulo operations and stores it in the buf array in reverse order. Finally, it creates a new String object using the String(char[], int, int) constructor, which takes the buf array, the starting position of the desired substring (which is pos), and the length of the desired substring (which is 11 - pos). The resulting String object is returned as the output of the valueOf() method.
Note that the actual implementation of the valueOf() method may vary depending on the version of Java you are using, as well as the specific input data and data type being converted.
Signature of Java String valueOf():
The valueOf() method in Java has several overloaded versions, each with a different signature depending on the type of data being converted. Here are some of the most common signatures:
public static String valueOf(boolean b) public static String valueOf(char c) public static String valueOf(char[] data) public static String valueOf(double d) public static String valueOf(float f) public static String valueOf(int i) public static String valueOf(long l) public static String valueOf(Object obj)
Each of these methods takes a different type of input and returns a String object representing that input. For example, valueOf(int i) takes an int value and returns a String object representing that value.
Note that some versions of the valueOf() method are static methods of the String class, while others are static methods of the Object class. The versions that are static methods of the Object class take an Object parameter and return a String object representing the string value of that object, which may involve calling the toString() method of the object.
Returns of Java String valueOf():
The valueOf() method in Java returns a String object that represents the input data that was converted to a string. The specific return value depends on the version of the valueOf() method being called and the type of input data being converted. Here are some examples:
String s1 = String.valueOf(123); // returns "123" String s2 = String.valueOf(true); // returns "true" String s3 = String.valueOf(3.14159); // returns "3.14159" String s4 = String.valueOf(new Object()); // returns a string representation of the Object
In each of these examples, the valueOf() method returns a String object representing the input data. Note that for some types of input data, such as objects, the specific string representation may depend on the implementation of the toString() method of the object being converted.
It’s important to note that the valueOf() method always returns a new String object, even if the input is already a String. For example, calling String.valueOf("hello") will return a new String object with the value “hello”, rather than simply returning the original input string.
Java String valueOf() method example:
Here’s an example of using the valueOf() method in Java to convert various data types to String objects:
int num = 42; double pi = 3.14159; boolean flag = true; String str1 = String.valueOf(num); // "42" String str2 = String.valueOf(pi); // "3.14159" String str3 = String.valueOf(flag); // "true"
In this example, we first declare three variables of different data types: an int, a double, and a boolean. We then use the valueOf() method to convert each of these variables to a String object.
The first call to valueOf() converts the int variable num to a String object str1 with the value “42”. The second call converts the double variable pi to a String object str2 with the value “3.14159”. The third call converts the boolean variable flag to a String object str3 with the value “true”.
Note that in each case, the valueOf() method returns a new String object that represents the input data. Also, the valueOf() method is a static method of the String class, so we call it using the class name String.valueOf().
Java String valueOf(boolean bol) Method Example:
Here’s an example of using the valueOf(boolean bol) method in Java to convert a boolean value to a String object:
boolean flag = true; String str = String.valueOf(flag); // "true"
In this example, we declare a boolean variable flag with the value true. We then use the valueOf(boolean bol) method to convert this boolean value to a String object str.
The valueOf(boolean bol) method takes a boolean input and returns a String object representing that input. In this case, the method returns a new String object with the value “true”.
Note that we could also use the Boolean.toString(boolean b) method to achieve the same result, like this:
boolean flag = true; String str = Boolean.toString(flag); // "true"
This method is a static method of the Boolean class and takes a boolean input and returns a String object representing that input. In this case, the method returns a new String object with the value “true”.
Java String valueOf(char ch) Method Example:
Here’s an example of using the valueOf(char ch) method in Java to convert a char value to a String object:
char ch = 'A'; String str = String.valueOf(ch); // "A"
In this example, we declare a char variable ch with the value 'A'. We then use the valueOf(char ch) method to convert this char value to a String object str.
The valueOf(char ch) method takes a char input and returns a String object representing that input. In this case, the method returns a new String object with the value “A”.
Note that we could also use the Character.toString(char c) method to achieve the same result, like this:
char ch = 'A'; String str = Character.toString(ch); // "A"
This method is a static method of the Character class and takes a char input and returns a String object representing that input. In this case, the method returns a new String object with the value “A”.
Java String valueOf(float f) and valueOf(double d):
Here are examples of using the valueOf() method in Java to convert a float and a double value to String objects:
float num1 = 3.14159f; double num2 = 2.71828; String str1 = String.valueOf(num1); // "3.14159" String str2 = String.valueOf(num2); // "2.71828"
In these examples, we declare a float variable num1 with the value 3.14159f and a double variable num2 with the value 2.71828. We then use the valueOf() method to convert each of these variables to a String object.
The first call to valueOf() converts the float variable num1 to a String object str1 with the value “3.14159”. The second call converts the double variable num2 to a String object str2 with the value “2.71828”.
Note that the valueOf() method takes a numeric input and returns a String object representing that input. The specific format of the output String depends on the input value and the implementation of the method.
It’s important to note that for float and double values, the output String may contain scientific notation. For example, calling String.valueOf(1.2345e-3) would return a String object with the value “0.0012345”.