If you are obtaining user input utilizing Java’s Scanner class, you may notice that the next(), nextInt(), nextDouble(), etc., is followed by the subsequent nextLine() appearing to be overlooked. This is a frequent mistake for Java beginners and typically leads to incomplete or inaccurate input processing.
So what is the origin of the issue? Why does nextLine() behave differently after invoking other Scanner methods? And more importantly, how can you resolve it? In this article, we’ll cover:
The inner mechanics of Scanner input methods
Why nextLine() is often avoided following next() or nextFoo()
Detailed solutions and code examples on how to handle it properly
The Java Scanner class is an inbuilt tool for collecting input from sources like the standard console input, a file, or a stream. It belongs to the java.util package and was introduced with Java 5 (Java SE 1.5). It simplifies the parsing of primitive types and strings using regular expressions.
With Scanner, Java developers can read various inputs utilizing methods such as:
next() – retrieves the next token (word) as a string
nextInt() retrieves the next token as an int
nextDouble() – retrieves the next token as a double.
nextLine() – retrieves an entire line of text
Comprehending the Scanner Input Dilemma in Java
It is typical for the Scanner class next() and nextFoo() methods, where Foo represents any primitive data type like Int, Double, etc., to bypass a newline character in the input because these methods are designed to read only a single token from the input. A token is defined as a series of characters that excludes any white space.
When the Scanner processes a token using one of the next() or nextFoo() methods, it consumes all the characters within the token, including the white space that follows the token but not the white space that precedes it.
If you have already executed a next() or nextFoo() method to capture a token from the input and wish to read the remainder of the line, you can invoke the nextLine() method immediately post the next() or nextFoo() method.
What’s the distinction between next() and nextLine()?
The next() Method: The next() method in Java exists within the Scanner class. It is employed to gather input from the user. To utilize this method, a Scanner object needs to be instantiated. This method reads input until a space(” “) is encountered.
The nextLine() Method: This method is utilized to collect input from the user until the end of the line, which means it takes input until a new line is introduced or the user presses enter.
In Java, next() and nextLine() function differently for reading input.
Example:
Java
Code Copied!
var isMobile = window.innerWidth “);
editor14722.setValue(decodedContent); // Set the default text
editor14722.clearSelection();
editor14722.setOptions({
maxLines: Infinity
});
function decodeHTML14722(input) {
var doc = new DOMParser().parseFromString(input, “text/html”);
return doc.documentElement.textContent;
}
// Function to copy code to clipboard
function copyCodeToClipboard14722() {
const code = editor14722.getValue(); // Get code from the editor
navigator.clipboard.writeText(code).then(() => {
jQuery(“.maineditor14722 .copymessage”).show();
setTimeout(function() {
jQuery(“.maineditor14722 .copymessage”).hide();
}, 2000);
}).catch(err => {
console.error(“Error copying code: “, err);
});
}
“““javascript
{
jQuery.ajax({
url: “https://intellipaat.com/blog/wp-admin/admin-ajax.php”,
type: “post”,
data: {
language: “java”,
code: code,
cmd_line_args: “”,
variablenames: “”,
action: “compilerajax”
},
success: function(response) {
var myArray = response.split(“~”);
var data = myArray[1];
jQuery(“.output14722”).html(“
"+data+"");
jQuery(".maineditor14722 .code-editor-output").show();
jQuery("#runBtn14722 i.run-code").hide();
}
})
}
function closeoutput14722() {
var code = editor14722.getSession().getValue();
jQuery(".maineditor14722 .code-editor-output").hide();
}
// Attach event listeners to the buttons
document.getElementById("copyBtn14722").addEventListener("click", copyCodeToClipboard14722);
document.getElementById("runBtn14722").addEventListener("click", runCode14722);
document.getElementById("closeoutputBtn14722").addEventListener("click", closeoutput14722);
Input:
Output:
Explanation: In the preceding code, when the next() function is invoked prior to the nextLine() function, the newline character remaining in the buffer leads to the nextLine() being bypassed. To rectify this, an additional scanner.nextLine(); should be utilized after the next() to capture the unwanted newline in the buffer, ensuring that the nextLine() functions properly for inputs with multiple words.
Why can’t You Use nextLine() or next() following nextInt() in Java?
The nextLine() function in Java’s Scanner class is not clearly understood by the user; its treatment of input varies compared to other Scanner methods such as nextInt(), next(), and nextDouble().
The issue arises when it follows other Scanner methods like next(), nextInt(), nextDouble(), etc.
Understanding the Problem
The nextLine() function captures all characters on the current line, including the newline character (n).
In contrast, other Scanner methods such as nextInt() and next() do not account for the newline character remaining in the buffer.
Consequently, nextLine() may appear to be “skipped” by the user’s input.
Example:
Java
Code Copied!
Input:
Output:
Clarification of the Adjusted Code: Now, the aforementioned Java program efficiently addresses the input issue by consuming the remaining newline character (n) following the scanner.nextInt() call. This ensures that scanner.nextLine() awaits the user’s input.
1. User Input
Enter an integer: 5
Enter your name: John Doe
2. Program Flow
When scanner.nextInt() is executed, it retrieves the integer; nextInt() only reads 5 but retains the newline (n) in the buffer.
When scanner.nextLine() is executed, it consumes the leftover newline. This eliminates the newline (n) left after nextInt().
When scanner.nextLine() is executed, it accurately captures the full name. Now, nextLine() waits for the user input instead of reading the residual newline.
Strategies to Avoid Scanner Skipping nextLine()
1. Consume the Remaining Newline
After utilizing nextInt(), nextDouble(), or next(), explicitly read the newline character by employing an additional nextLine() method.
Instance:
Java
Code Copied!
var isMobile = window.innerWidth ");
editor52852.setValue(decodedContent); // Set the default text
editor52852.clearSelection();
editor52852.setOptions({
maxLines: Infinity
});
function decodeHTML52852(input) {
var doc = new DOMParser().parseFromString(input, "text/html");
return doc.documentElement.textContent;
}
// Function to copy code to clipboard
function copyCodeToClipboard52852() {
const code = editor52852.getValue(); // Retrieve code from the editor
navigator.clipboard.writeText(code).then(() => {
jQuery(".maineditor52852 .copymessage").show();
setTimeout(function() {
jQuery(".maineditor52852 .copymessage").hide();
}, 2000);
}).catch(err => {
console.error("Issue copying code: ", err);
});
}
data: {
language: "java",
code: code,
cmd_line_args: "",
variablenames: "",
action:"compilerajax"
},
success: function(response) {
var myArray = response.split("~");
var data = myArray[1];
jQuery(".output52852").html("
"+data+"");
jQuery(".maineditor52852 .code-editor-output").show();
jQuery("#runBtn52852 i.run-code").hide();
}
})
}
function closeOutput52852() {
var code = editor52852.getSession().getValue();
jQuery(".maineditor52852 .code-editor-output").hide();
}
// Bind event listeners to the buttons
document.getElementById("copyBtn52852").addEventListener("click", copyCodeToClipboard52852);
document.getElementById("runBtn52852").addEventListener("click", executeCode52852);
document.getElementById("closeoutputBtn52852").addEventListener("click", closeOutput52852);
``````html
Input:
Output:
Explanation: The aforementioned Java application captures a digit and a name from the user. As nextInt() does not consume the newline character, nextLine() is utilized subsequently to clear it, which prevents the input from being bypassed and ensures the name is accurately recorded.
2. Capture the Entire Line and Analyze the Input
Instead of employing nextInt(), capture the complete line using nextLine() and then convert it to an integer utilizing the Integer.parseInt() method.
Example:
Java
Code Copied!
Input:
Output:
Explanation: The preceding Java program is designed to read a digit from the user using the Scanner class. Rather than utilizing the nextInt() method, it captures the full line with the nextLine() method and converts it into an integer using Integer.parseInt(). This prevents nextLine() from being missed due to remaining newline characters. In the end, it prints the digit and closes the Scanner to avoid resource leaks.
3. Utilize Only nextLine() for All Inputs
Another strategy is to apply nextLine() for every input (including numbers) and manually process them. This completely circumvents the issue.
Example:
Java
Code Copied!
Input:
Output:
Explanation: This application guarantees effective input processing by receiving a number as a string, converting it into an integer, and requesting the user's name utilizing nextLine(). By employing nextLine() for all inputs, it averts skipping complications. Ultimately, it presents the user's name and number.
In Java, delimiters and string tokenization play a crucial part in how the next() and nextLine() methods accept the input.
The next() method identifies whitespaces such as spaces, tabs, or newlines as its delimiters. It processes the input word by word and halts at the first space. Thus, if the user types "John Doe," next() will recognize "John," leaving the "Doe" in the buffer.
In contrast, the nextLine() method interprets the newline character (n) as its delimiter and captures the entire line as a singular string. For custom delimiters, the scanner class incorporates the useDelimiter() method, which allows for defining separators such as commas or semicolons.
For instance, utilizing scanner.useDelimiter(",") will enable reading the input and segmenting it by commas instead of spaces, proving beneficial for parsing organized data like CSV files.
function closeoutput16165() {
var code = editor16165.getSession().getValue();
jQuery(".maineditor16165 .code-editor-output").hide();
}
// Attach event listeners to the buttons
document.getElementById("copyBtn16165").addEventListener("click", copyCodeToClipboard16165);
document.getElementById("runBtn16165").addEventListener("click", runCode16165);
document.getElementById("closeoutputBtn16165").addEventListener("click", closeoutput16165);
Output:
Explanation:In the preceding code, the delimiter is designated as the “,” (comma) through the scanner.useDelimiter(",", method, which enables the input to be divided based on commas instead of spaces. The next() function is utilized to obtain each token until a comma appears, while (scanner.hasNext()) guarantees that all tokens are processed. However, unlike the nextLine() function, which retrieves the entire line as one string. For instance, if the input is given as "apple, banana, grape, orange", the next() captures "apple", then proceeds to "banana", and continues until all tokens are gathered.
Best Practices for Using a Scanner.nextLine() After Other next() Methods
1. Always Consume the Remaining Newline After next(), nextInt(), etc.
Since functions like nextInt(), nextDouble(), and next() do not process the newline (n), it’s advisable to use scanner.nextLine(); immediately after employing them.
2. Utilize the nextLine() Method for Multi-Word Input
If the user is required to enter a complete sentence such as an address or name with spaces, apply the nextLine() instead of next().
3. Employ nextLine() for Mixed Data Types
When receiving both numbers and strings, it is safer to use nextLine() and subsequently parse the numbers.
4. Use Custom Delimiters When Necessary
If input is separated by commas or additional characters, establish a custom delimiter rather than using the default of spaces.
5. Always Close the Scanner
Closing the Scanner after use releases system resources.
Note: Avoid closing Scanner(System.in) if reading input multiple times, as it will terminate System.in and restrict further input.
Conclusion
From the above, we deduce that the Scanner class bypasses the nextLine() method following the next() or nextFoo() because these methods do not capture the newline (n) character, compelling nextLine() to pick up the remaining newline rather than waiting for user input. To remedy this, the scanner.nextLine(); method should be added after nextFoo(). Understanding the distinction between next() and nextLine(), using custom delimiters, and adhering to best practices can avert input problems.
If you wish to explore more about Java, you can refer to our Java Course.
Why is the Scanner Skipping nextLine After Utilizing next or nextFoo - FAQs
Q1. What distinguishes the next() and the nextLine() function?
The next() function reads input until a whitespace is found, while nextLine() reads input up to a newline character.
Q2. What does the Scanner nextLine() accomplish?
The nextLine() function returns all text until a line break occurs.
Q3. Does nextLine return a string?
The nextLine() function returns a string containing all characters up to the next newline character in the scanner or until the end of the scanner if there are no subsequent newline characters.
Q4. How can I advance to the next line in Java?
In Java, n signifies an escape sequence that represents a newline character. It’s used to insert a line break or initiate a new line in strings or output.
Q5. What occurs if nextLine() is invoked after nextInt()?
The nextInt() function only consumes the integer portion while leaving behind the enter or newline character
``````html
in the input buffer. When the third scanner's nextLine() function is activated, it detects the enter or newline character still present in the input buffer, misinterprets it as user input, and returns at once.
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