Cannot be resolved to a variable java ошибка

This guide will teach you how to fix the cannot be resolved to a variable error in Java.

For this, you need to understand the scope of a programming language. Keep reading this compact guide to learn more and get your fix to this error.

Fix the cannot be resolved to a variable Error in Java

In Java programming language, we use curly brackets {} to identify the scope of a class, functions, and different methods.

For instance, take a look at the following code:

public static void calculateSquareArea(int x)
{
    System.out.println(x*x);
}

In the above code example, the scope of the variable x is limited within the curly brackets {}. You cannot call or use it outside this scope. If you try, the cannot be resolved to a variable error will come out.

It means it cannot detect the initialization of variables within its scope. Similarly, if you make a private variable, you cannot call it inside a constructor.

Its scope is out of bounds. Here’s the self-explanatory code.

public class Main 
{
    public static void main(String args[]) 
    {
        int var  =3;  
        // scope is limited within main Block;
        // The Scope of var Amount Is Limited..........
        // Accessible only Within this block............
    }
    public static void Calculate (int amount)
    {
      // The Scope of Variable Amount Is Limited..........
      // Accessible only Within this block............
    }
}

I’m a complete beginner to Java, and after learning some of the basics, I decided to do some practice problems. The one I settled on is to create a program that asks for your name, then will only greet you if your name is Alice or Bob. Here’s what I have so far.

I’ve searched for solutions on various forums, but none them seem to be having the same problem. Here is my code:

import java.util.Scanner;

public class codingchallenge {

	public static void main(String[] args) {
		
		System.out.println("Hello, what is your name?");
		Scanner name = new Scanner(System.in);
		System.out.println(name.nextLine());
		name.close();
			if (name == Alice) {
				System.out.println("Hello, Alice");
			}
			
			else if (name == Bob){
				System.out.println("Hello, Bob");
			}
			else {
				System.out.println("Your name isn't Alice or Bob!");
			}
		name.close();
	}
}

And here is was the compiler says:

Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
	Alice cannot be resolved to a variable
	Bob cannot be resolved to a variable

Thanks to everyone who helps out in advance!

эту переменную определяют после

long n12 = (int) (upc%10);
upc /= 10;
long n11 = (int) (upc%10);
upc /= 10;
long n10 = (int) (upc%10);
upc /= 10;
long n9 = (int) (upc%10);
upc /= 10;
long n8 = (int) (upc%10);
upc /= 10;
long n7 = (int) (upc%10);
upc /= 10;
long n6 = (int) (upc%10);
upc /= 10;
long n5 = (int) (upc%10);
upc /= 10;
long n4 = (int) (upc%10);
upc /= 10;
long n3 = (int) (upc%10);
upc /= 10;
long n2 = (int) (upc%10);
upc /= 10;
long n1 = (int) (upc%10);



int m = (n2 + n4 + n6 + n8 + n10);
long n = (n1 + n3 + n5 + n7 + n9 + n11);
long r = (10-(m+3*n)%10);

вы используете эту переменную, которая не была определена, и после использования вы определяете эти переменные

Изменить: если

Когда вы определяете свой метод с возвращаемым значением в течение длительного времени и возвращаете значение String, см. Возвращаемое значение

return (upc + " is a feasible UPC code"); 

вам нужно изменить тип возвращаемого значения либо в методе, либо в качестве времени возврата, например, если вы хотите вернуть это, тогда подпись метода выглядит так

public long getUpc(){
  // and return will work
  return (upc + " is a feasible UPC code"); 
}

но если вы хотите использовать только числовое значение, не меняйте его подпись метода, просто верните upc, как это

return upc;

the compiler says

Exception in thread «main» java.lang.Error: Unresolved compilation problems:

i cannot be resolved to a variable

i cannot be resolved to a variable

i cannot be resolved to a variable

i cannot be resolved to a variable

i cannot be resolved to a variable

at minimusikplayer2.MiniMusikPlayer2.los(MiniMusikPlayer2.java:25)

at minimusikplayer2.MiniMusikPlayer2.main(MiniMusikPlayer2.java:9)

I will be thankfull for any support. Now I have to go but I will be back in 5 hours!!!

The problems are in line 25,26 and 27

package minimusikplayer2;

import javax.sound.midi.*;

public class MiniMusikPlayer2 implements ControllerEventListener {

public static void main(String[] args) {

MiniMusikPlayer2 mini = new MiniMusikPlayer2();

mini.los();

}

public void los() {

try {

Sequencer sequencer = MidiSystem.getSequencer();

sequencer.open();

int[] gewuenschteEvents = {127

};

sequencer.addControllerEventListener(this, gewuenschteEvents);

Sequence seq = new Sequence(Sequence.PPQ, 4);

Track track = seq.createTrack();

for (int i = 5; i < 60; i+= 4); {

track.add(eventErzeugen(144,1,i,100,i));

track.add(eventErzeugen(176,1,127,0,i));

track.add(eventErzeugen(128,1,i,100,i + 2));

}

sequencer.setSequence(seq);

sequencer.setTempoInBPM(220);

sequencer.start();

Thread.sleep(5000);

sequencer.close();

}catch (Exception ex) {ex.printStackTrace();}

}

public void controlChange(ShortMessage event) {

System.out.println(«la»);

}

public MidiEvent eventErzeugen(int comd, int chan, int one, int two, int tick){

MidiEvent event = null;

try{

ShortMessage a = new ShortMessage();

a.setMessage(comd,chan,one,two);

event = new MidiEvent(a, tick);

}catch (Exception e){}

return event;