Scanner Class in Java
Scanner is a class in java.util package used for obtaining the input of the primitive types like int, double, etc. and strings. It is the easiest way to read input in a Java program, though not very efficient if you want an input method for scenarios where time is a constraint like in competitive programming.
- To create an object of Scanner class, we usually pass the predefined object System.in, which represents the standard input stream. We may pass an object of class File if we want to read input from a file.
- To read numerical values of a certain data type XYZ, the function to use is nextXYZ(). For example, to read a value of type short, we can use nextShort()
- To read strings, we use nextLine().
- To read a single character, we use next().charAt(0). next() function returns the next token/word in the input as a string and charAt(0) function returns the first character in that string.
- The Scanner class reads an entire line and divides the line into tokens. Tokens are small elements that have some meaning to the Java compiler. For example, Suppose there is an input string: How are you
In this case, the scanner object will read the entire line and divides the string into tokens: “How”, “are” and “you”. The object then iterates over each token and reads each token using its different methods.
Let us look at the code snippet to read data of various data types.
Geek F 40 9876543210 9.9
Name: Geek Gender: F Age: 40 Mobile Number: 9876543210 CGPA: 9.9
Sometimes, we have to check if the next value we read is of a certain type or if the input has ended (EOF marker encountered).
Then, we check if the scanner’s input is of the type we want with the help of hasNextXYZ() functions where XYZ is the type we are interested in. The function returns true if the scanner has a token of that type, otherwise false. For example, in the below code, we have used hasNextInt(). To check for a string, we use hasNextLine(). Similarly, to check for a single character, we use hasNext().charAt(0).
Let us look at the code snippet to read some numbers from the console and print their mean.
1 2 3 4 5 a
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