Android Studio：随机数生成器反复返回0s

Question

I'm currently taking an online course in Java using Android Studio. As part of the course we had an exercise to build Higher or Lower number guessing game. The initial code I wrote worked just fine (despite being a bit wordy, but I'm still learning), it generated a random number and everything worked right with all the correct messaging. Here is the working code.

import java.util.Random;

public class MainActivity extends AppCompatActivity {

        Random ran = new Random();
        int gameStart = 1 + (int) (Math.random() * (30));

    public void buttonClick(View view) {
        EditText number = (EditText) findViewById(R.id.number);
        Button button = (Button) findViewById(R.id.button);
        int num = Integer.parseInt(number.getText().toString());


        if (num == gameStart) {

            Toast.makeText(this, "Correct!", Toast.LENGTH_SHORT).show();

        } else if (num > gameStart) {

            Toast.makeText(this, "Lower", Toast.LENGTH_SHORT).show();
        } else {

            Toast.makeText(this, "Higher", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        }
    }

But then the instructor has introduced extra code to make game restart if the answer is correct with a new number by making Random a method and adding it in the initial if statement. In the video it worked but when I added it and compiled the only number Random generates is 0. I have tried everything but for the love of god can't get it to work correctly. Can someone please have a look at the changes below and spot what could be creating this issue? What needs to be ammended?

public class MainActivity extends AppCompatActivity {

    int gameStart;

    public void gameRestart() {

        Random ran = new Random();
        int gameStart = 1 + (int) (Math.random() * (30));

    }
    public void buttonClick(View view) {
        EditText number = (EditText) findViewById(R.id.number);
        Button button = (Button) findViewById(R.id.button);
        int num = Integer.parseInt(number.getText().toString());


        if (num == gameStart) {

            Toast.makeText(this, "Correct!", Toast.LENGTH_SHORT).show();
            gameRestart();

        }

Answer 1

 int gameStart;

    public void gameRestart() {    
        Random ran = new Random();
        int gameStart = 1 + (int) (Math.random() * (30));    
    }

you never alter the value of instance variable gameStart, so it keeps the default value, which is 0. You create a local variable gameStart in your constructor, which isn't used afterwards.

Alter your code to this to set the instance variable:

 int gameStart;

    public void gameRestart() {
        Random ran = new Random();
        gameStart = 1 + (int) (Math.random() * (30));
    }

EDIT: as @AndyTurner remarked: you 're also not using your ran instance of the Random class, so you can delete that variable as well.

Answer 2

public void gameRestart() {
    Random ran = new Random();
    int gameStart = 1 + (int) (Math.random() * (30));
}

Here, I suppose you want to store your random value inside the member variable called gameStart . It is not the case because you redefine a local variable with the same number in the method. You just have to delete the int before your variable (and delete the ran line because unused)

public void gameRestart() {
    gameStart = 1 + (int) (Math.random() * (30));
}

Answer 3

you can try this;

final int random = new Random().nextInt(50) + 30; 
// it will generate random number between 30 & 80