Checking if EditText.isEmpty() not working

问题

In my code, I want to check if the password field is empty. I am using the isEmpty() method to accomplish it but it does not work. Leaving the password field blank, reverts to the 2nd else-if statement and not the third.

public class MainActivity extends Activity {


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

    final EditText password = (EditText) findViewById(R.id.editText_Password);
    Button enter = (Button) findViewById(R.id.button);

    enter.setOnClickListener(new OnClickListener() {



        @Override
        public void onClick(View arg0) {

            String user_pass;
            user_pass = password.getText().toString();

                if (user_pass.equals("123")) {
                    Toast.makeText(MainActivity.this, "Welcome!", Toast.LENGTH_SHORT).show();
                    Intent I = new Intent("com.mavenmaverick.password.OKActivity");
                    startActivity(I);
                }

                else

                    if(user_pass != "123"){
                    Toast.makeText(MainActivity.this, "Incorrect", Toast.LENGTH_SHORT).show();
                    AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(MainActivity.this);
                        dialogBuilder.setIcon(R.drawable.ic_launcher);
                        dialogBuilder.setTitle("Oops!");
                        dialogBuilder.setMessage("Incorrect Password");
                        dialogBuilder.setPositiveButton("OK", null);
                        dialogBuilder.show();
                    }

                else
                    if (user_pass.isEmpty()) {
                        AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(MainActivity.this);
                            dialogBuilder.setIcon(R.drawable.ic_launcher);
                            dialogBuilder.setTitle("Oops!");
                            dialogBuilder.setMessage("Password Field Cannot Be Empty");
                            dialogBuilder.setPositiveButton("OK", null);
                            dialogBuilder.show();
                        }

        }
    });




}

回答1:

Your second if checks for user_pass != "123". Logically, if the user_pass is empty it is not "123" and it won't even go for the third if. If you want it to work, switch your second and third if.

回答2:

if (string == "aString") {
    ...
} else if (string != "somestring") {
    ...
} else if (string.isEmpty()) {
    ...
}

This won't check if the string is empty, it will stop on the 2nd if block since it's not equal.

To avoid this, check if it's empty first. Also don't use == when comparing string values:

if (user_pass.isEmpty()) {
    // It's empty
} else if (user_pass.equals("123")) {
    // Equals
} else if (!user_pass.equals("123")){
    // Not equals
}

回答3:

Wrong String comparison with operators. For string comparison, you can use .equals() method.

By the way for your case,

just use,

if (user_pass.isEmpty()) {
      displayAlertDialog("Password Field Cannot Be Empty");
}else if(user_pass.equals("123"))
{
 Toast.makeText(MainActivity.this, "Welcome!", Toast.LENGTH_SHORT).show();
 Intent I = new Intent("com.mavenmaverick.password.OKActivity");
 startActivity(I);

}else
{
Toast.makeText(MainActivity.this, "Incorrect", Toast.LENGTH_SHORT).show();
    displayAlertDialog("Incorrect Password");               
}

private void displayAlertDialog(String message)
{
 AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(MainActivity.this);
                            dialogBuilder.setIcon(R.drawable.ic_launcher);
                            dialogBuilder.setTitle("Oops!");
                            dialogBuilder.setMessage(message);
                            dialogBuilder.setPositiveButton("OK", null);
                            dialogBuilder.show();
}