Cannot make a static reference to the non-static method getReadableDatabase() from the type SQLiteOpenHelper

public static boolean vaidateUser(String username, String password) {
        Cursor c = getReadableDatabase().rawQuery(
                "SELECT * FROM " + TABLE_NAME_CREDENTIALS + " WHERE "
                        + COLUMN_NAME_USERNAME + "='" + username +"'AND "+COLUMN_NAME_PASSWORD+"='"+password+"'" ,  null);
       if (c.getCount()>0)
          return true;
          return false;

lsLogin.setOnClickListener (new OnClickListener() {

                @Override
                public void onClick(View v) {
                    //check login
                    String username = lsUsername.getText().toString();
                    String password = lsPassword.getText().toString();
                    try{
                        if(LoginDB.vaidateUser(username,password)) {
                            Intent goToNextActivity = new Intent(getApplicationContext(), menu.class);
                            startActivity(goToNextActivity);

                                Toast.makeText(LoginScrExample.this,"Login Sucessful",Toast.LENGTH_LONG).show();
                            }else{
                                Toast.makeText(LoginScrExample.this,"Invalid Username/Password",Toast.LENGTH_LONG).show();
                            }

                            }

getReadableDatabase();

Cursor c = new SQLiteOpenHelper().getReadableDatabase()..

SQLiteOpenHelper soh = new SQLiteOpenHelper();
Cursor c = soh().getReadableDatabase()..