Button intent to next activity.

Button intent

import android.app.Activity;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

//Button id = buttonBack
//Next activity name = loginActivity

public class signupActivity extends AppCompatActivity {
    private Button buttonBack;

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

        buttonBack = (Button) findViewById(R.id.buttonBack);
        buttonBack.setOnClickListener(View.OnClickListener() {
            @Override
            public void onClick (View v){
                openLogin() {
                }
            }
        });
        public void openLogin () {
            Intent intent = new Intent(this, loginActivity.class);
            startActivity(intent);
        }
    }
}

buttonBack.setOnClickListener(this);

So you need an onclick method which listens for the id of the pressed button.

Okay I get it now.

This method is a class method.
public void onClick(View v) {
if(v == findViewById(R.id.Button1)){
//do here what u wanna do.
}
else if(v == findViewById(R.id.Button2)){
//do here what u wanna do.
}
else if(v == findViewById(R.id.Button3)){
//do here what u wanna do.
}
}