Programming Tutorials

valueOf() in Java

By: Emiley J in Java Tutorials on 2007-09-02  

The valueOf() method converts data from its internal format into a human-readable form. It is a static method that is overloaded within String for all of Java's built-in types, so that each type can be converted properly into a string. valueOf() is also overloaded for type Object, so an object of any class type you create can also be used as an argument. (Recall that Object is a superclass for all classes.)

Here are a few of its forms:

static String valueOf(double num)
static String valueOf(long num)
static String valueOf(Object ob)
static String valueOf(char chars[ ])

As we discussed earlier, valueOf() is called when a string representation of some other type of data is needed—for example, during concatenation operations. You can call this method directly with any data type and get a reasonable String representation. All of the simple types are converted to their common String representation. Any object that you pass to valueOf() will return the result of a call to the object's toString() method. In fact, you could just call toString() directly and get the same result.

For most arrays, valueOf() returns a rather cryptic string, which indicates that it is an array of some type. For arrays of char, however, a String object is created that contains the characters in the char array. There is a special version of valueOf() that allows you to specify a subset of a char array. It has this general form:

static String valueOf(char chars[ ], int startIndex, int numChars)

Here, chars is the array that holds the characters, startIndex is the index into the array of characters at which the desired substring begins, and numChars specifies the length of the substring.

// Using valueOf() method for Integer class
int i = 100;
Integer intObj = Integer.valueOf(i); // returns an Integer object representing the value of i

// Print the value of Integer object
System.out.println("Value of Integer object: " + intObj); // Output: Value of Integer object: 100

In this example, we first declare an int variable i and initialize it to 100. We then use the valueOf() method of the Integer class to convert the int value to an Integer object intObj.

We can also use the valueOf() method for other primitive types such as Double, Float, Long, Short, Byte, Character, and Boolean. For example, here's how we can use valueOf() for the Double class:

// Using valueOf() method for Double class
double d = 3.14159;
Double doubleObj = Double.valueOf(d); // returns a Double object representing the value of d

// Print the value of Double object
System.out.println("Value of Double object: " + doubleObj); // Output: Value of Double object: 3.14159