java - 尝试访问类时出现空指针异常

Question

我正在尝试从我的方法中获取值并将其显示在另一个类中作为 toast (只是为了确保我的方法有效)。我收到一个我似乎无法弄清楚的空指针异常，我尝试了多种不同的方法。我什至尝试给我的字符串值“This”和“That”。然后我的日志猫告诉我

04-05 21:17:29.633: E/AndroidRuntime(18838): java.lang.RuntimeException: 无法启动 Activity ComponentInfo{com.cerealBarApps/com.cerealBarApps.Testing}: android.content.res.Resources$ NotFoundException:字符串资源 ID #0x0

这是我想用来运行所有内容的类。

public class Testing extends Activity {

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        String Testeroni = "This";
        String Testerhynocerous = "That";

        LoginTest test = new LoginTest();

        Toast.makeText(getApplicationContext(), (test.TestUsername(Testeroni)),
                Toast.LENGTH_SHORT).show();

        Toast.makeText(getApplicationContext(),
                (test.TestPassword(Testerhynocerous)), Toast.LENGTH_SHORT)
                .show();

    }
}

这是我调用以从中运行方法的类。

public class LoginTest {

    // 0 = Username length is less than 4 or greater than 15
    // 1 = Username character is not a letter/or digit
    // 9 = Everything is okay in username :)
    public int TestUsername(String username) {
        if (username.length() <= 4 || username.length() >= 15) {

            return 0;
        }

        for (int i = 0; i < username.length(); i++) {
            if (Character.isDigit(username.charAt(i))
                    || Character.isJavaLetter(username.charAt(i))) {
                System.out.println("");
                // Do Nothing
            } else

                return 1;
        }
        return 9;
    }



        // 2 = Passowrd length is less than 4 or greater than 15
        // 3 = Password character is not a digit
        // 8 = Everything is okay in password :)
        public int TestPassword(String password) {
            if (password.length() <= 4 || password.length() >= 15) {
                return 2;
            }

            for (int i = 0; i < password.length(); i++) {
                if (Character.isDigit(password.charAt(i))
                        || Character.isJavaLetter(password.charAt(i))) {
                    System.out.println("");
                    // Do Nothing
                } else
                    return 3;
            }
            return 8;
        }
    }

Answer 1

这些代码:

Toast.makeText(getApplicationContext(), (test.TestUsername(Testeroni)),
            Toast.LENGTH_SHORT).show();

    Toast.makeText(getApplicationContext(),
            (test.TestPassword(Testerhynocerous)), Toast.LENGTH_SHORT)
            .show();

有一些问题，test.TestUsername(Testeroni) 和 test.TestPassword(Testerhynocerous) 返回类型是 int，所以它认为像字符串 res id，所以如果可以更改为:

 Toast.makeText(getApplicationContext(), (""+test.TestUsername(Testeroni)),
            Toast.LENGTH_SHORT).show();

    Toast.makeText(getApplicationContext(),
            (""+test.TestPassword(Testerhynocerous)), Toast.LENGTH_SHORT)
            .show();