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How do I accept the user input and put it into the while condition

This is my code, the while loop does not have an input and the rep variable does not accept an input:
import java.util.Scanner;
public class MixedData {
public static void main(String[] args) {
String rep = "";
do {
Scanner keyboard = new Scanner(System.in);
System.out.print("Enter your full name");
String name = keyboard.nextLine();
System.out.print("Enter your GPA: ");
double gpa = keyboard.nextDouble();
System.out.println("Name: " + name + ", GPA: " + gpa);
System.out.println("Do you want to enter the data for another student?(y/n)");
rep = keyboard.nextLine();
} // This does not accept input
while (rep.equals("y"));
}
}

Either just add one more keyboard.nextLine() before rep = keyboard.nextLine(); (in order to clear the newline character), or read your double gpa value with:
double gpa = Double.parseDouble(keyboard.nextLine());
Important point to understand here (especially if you're a novice Java developer), about why your code doesn't work, is, that you invoke nextDouble() as a last method on your Scanner instance, and it doesn't move the cursor to the next line.
A bit more details:
All the methods patterned nextX() (like nextDouble(), nextInt(), etc.), except nextLine(), read next token you enter, but if the token isn't a new line character, then the cursor isn't moved to the next line. When you enter double value and hit Enter, you actually give to the input stream two tokens: a double value, and a new line character, the double value is initialized into the variable, and the new line character stays into input stream. The next time you invoke nextLine(), that very new line character is read, and that's what gives you an empty string.

Here's the same code using a while loop instead of do-while. It works the way you want it to.
import java.util.Scanner;
public class MixedData {
public static void main(String[] args) {
String rep = "y";
while (!rep.equals("n")) {
Scanner keyboard = new Scanner(System.in);
System.out.print("Enter your full name: ");
String name = keyboard.nextLine();
System.out.print("Enter your GPA: ");
double gpa = keyboard.nextDouble();
System.out.println("Name: " + name + ",GPA: " + gpa);
System.out.println("Do you want to enter the data for another student?(y/n)");
rep = keyboard.next();
}
}
}

You need to skip blank lines.
public static void main(String[] args) {
String rep;
Scanner keyboard = new Scanner(System.in);
do {
System.out.print("Enter your full name");
String name = keyboard.nextLine();
System.out.print("Enter your GPA: ");
double gpa = keyboard.nextDouble();
System.out.println("Name: " + name + ", GPA: " + gpa);
System.out.println("Do you want to enter the data for another student?(y/n)");
rep = keyboard.next();
keyboard.skip("\r\n"); // to skip blank lines
}
while (rep.equalsIgnoreCase("y"));
keyboard.close();
}

Use nextLine instead of nextDouble:
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
String rep = "";
do {
System.out.println("Enter your full name:");
String name = keyboard.nextLine();
System.out.println("Enter your GPA:");
// double gpa = keyboard.nextDouble();
double gpa = Double.parseDouble(keyboard.nextLine());
System.out.println("Name: " + name + ", GPA: " + gpa);
System.out.println("Do you want to enter the data for another student?(y/n)");
rep = keyboard.nextLine();
} while (rep.equals("y"));
keyboard.close();
}

How to make "un-entered" user input show "not available" -- Java

I am just a beginner, so any help would be appreciated.
So here is my code:
import java.util.Scanner;
public class AccountScanner {
public static void main (String[] args) {
String name, course;
int age;
Scanner input = new Scanner(System.in);
System.out.print("Enter name: ");
name = input.nextLine();
System.out.print("Enter age: ");
age = input.nextInt();
System.out.print("Enter Course: ");
course = input.next();
System.out.println();
System.out.println("Name:" +name);
System.out.println("Age:" +age);
System.out.println("Course:" +course);
System.exit(0);
}
}
but what if the user did enter one of the details. What can I do to make it display "Not Available" instead
example:
enter name: Zack
enter age:
enter course: BSCS
output would be:
Name: Zack
Age: Not available
Course: BSCS

You can use a conditional operator to check if the inputs are empty and show the result correspondingly as follows:
String name, course, age;
Scanner input = new Scanner(System.in);
System.out.print("Enter name: ");
name = input.nextLine();
System.out.print("Enter age: ");
age = input.nextLine();
System.out.print("Enter Course: ");
course = input.nextLine();
System.out.println();
System.out.println("Name:" +(name.isEmpty()?"Not Available":name));
System.out.println("Age:" +(age.isEmpty()?"Not Available":new Integer(age)));
System.out.println("Course:" +(course.isEmpty()?"Not Available":course));
System.exit(0);

Java! How to go to the specific line?

I just started to code in Java and I have a question. After my "else" statement, I want to repeat my code again. How do I do that? Is there a keyword or something?
import java.util.Scanner;
public class UserInputStory {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
userinput:
System.out.println("Enter you name:");
String name = input.nextLine();
System.out.println("OK! Now enter your age:");
int age;
age = input.nextInt();
System.out.println("Good! And the city you live in, please:");
Scanner in = new Scanner(System.in);
String city = in.nextLine();
System.out.println("So, let's check");
System.out.println(
"Your name is " + name + ". You are " + age + " years old and you currently live in " + city + ".");
System.out.println("Is that right?");
Scanner inp = new Scanner(System.in);
String yesno = inp.nextLine();
if (yesno.equals("yes") || yesno.equals("Yes") || yesno.equals("YES")) {
System.out.println("Great job!");
}
else {
System.out.println("Let's try again then!");
}
}
}

Place the body of your code that you want repeating inside a while loop and break when your end-condition is true:
public static void main(String[] args) {
while(true) {
Scanner input = new Scanner(System.in);
userinput:
System.out.println("Enter you name:");
String name = input.nextLine();
System.out.println("OK! Now enter your age:");
int age;
age = input.nextInt();
System.out.println("Good! And the city you live in, please:");
Scanner in = new Scanner(System.in);
String city = in.nextLine();
System.out.println("So, let's check");
System.out.println("Your name is " + name + ". You are " + age + " years old and you currently live in " + city + ".");
System.out.println("Is that right?");
Scanner inp = new Scanner(System.in);
String yesno = inp.nextLine();
if (yesno.equals("yes") || yesno.equals("Yes") || yesno.equals("YES")) {
System.out.println("Great job!");
break;
}
else {
System.out.println("Let's try again then!");
}
}
}

You can envelop our whole code by:
while(1)
ut its not a good approach and there must be some condition applied (depending upon the xontext of your program) which can take you out of the loop

Trouble using nextInt and nextLine()

It's not letting me put my name in but it does the age works fine.
I know i can change the order of the statements but is there another way I could do it?
import java.util.Scanner;
public class ScannerErr2
{
public static void main(String [] args)
{
Scanner keyboard= new Scanner(System.in);
String name;
int age;
System.out.print("Enter your age : ");
age= keyboard.nextInt();
System.out.print("Enter your name: ");
name= keyboard.nextLine();
System.out.println("Age : "+age);
System.out.println("Name: "+name);
}
}

You problem is that the next int doesn't consider the new line character which goes in the input for your name part. Hence name is returned as blank.
You can change your code in 2 ways:
System.out.print("Enter your age : ");
age = keyboard.nextInt();
keyboard.nextLine();
System.out.print("Enter your name: ");
name = keyboard.nextLine();
or
System.out.print("Enter your age : ");
age = Integer.parseInt(keyboard.nextLine().trim());
System.out.print("Enter your name: ");
name = keyboard.nextLine();
I personally like the second way.

Runtime error - skipping a line of user input (Scanner)

In my tester file, I am trying to receive 3 inputs from the user however only 2 of the inputs are received and it seems that the program is skipping over the in.nextLine() line of code. Here is my code:
import java.util.Scanner;
public class IngredientTester
{
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
/*These 3 inputs work */
System.out.println("Please enter Ingredient name.");
String inputName = in.nextLine();
System.out.println("Please enter Ingredient measurement type.");
String inputType = in.nextLine();
System.out.println("Please enter Ingredient amount");
double inputAmount = in.nextDouble();
Ingredient inputIngredient = new Ingredient(inputName,inputType,inputAmount);
System.out.println(inputIngredient.getName() + "- " + inputIngredient.getAmount() + " " + inputIngredient.getMeasurement());
System.out.println("Please enter Ingredient name.");
inputName = in.nextLine();
/* ^ the input above does not work, but the ones below do work */
System.out.println("Please enter Ingredient measurement type.");
inputType = in.nextLine();
System.out.println("Please enter Ingredient amount");
inputAmount = in.nextDouble();
inputIngredient.setAmount(inputAmount);
inputIngredient.setName(inputName);
inputIngredient.setMeasurement(inputType);
System.out.println(inputIngredient.getName() + "- " + inputIngredient.getAmount() + " " + inputIngredient.getMeasurement());
}
}

The problem is that you are using:
double inputAmount = in.nextDouble();
which not only reads your first input amount but passes the carriage return to the next readLine statement.
The solution is to consume the carriage return first:
double inputAmount = Double.parseDouble(in.nextLine());