android studio实现登录注册界面，请给出完整代码

由于登录注册界面需要涉及到后端服务器的接口调用，所以完整代码无法提供，但是我可以给你提供一个基本框架的代码，供你参考：

activity_login.xml

<LinearLayout
    android:orientation="vertical"
    ...>

    <EditText
        android:id="@+id/et_username"
        ... />

    <EditText
        android:id="@+id/et_password"
        ... />

    <Button
        android:id="@+id/btn_login"
        ... />

    <TextView
        android:id="@+id/tv_register"
        ... />
</LinearLayout>

activity_register.xml

<LinearLayout
    android:orientation="vertical"
    ...>

    <EditText
        android:id="@+id/et_username"
        ... />

    <EditText
        android:id="@+id/et_password"
        ... />

    <EditText
        android:id="@+id/et_confirm_password"
        ... />

    <Button
        android:id="@+id/btn_register"
        ... />

    <TextView
        android:id="@+id/tv_login"
        ... />
</LinearLayout>

LoginActivity.java

public class LoginActivity extends AppCompatActivity {

    private EditText etUsername;
    private EditText etPassword;
    private Button btnLogin;
    private TextView tvRegister;

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

        etUsername = findViewById(R.id.et_username);
        etPassword = findViewById(R.id.et_password);
        btnLogin = findViewById(R.id.btn_login);
        tvRegister = findViewById(R.id.tv_register);

        btnLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // 点击登录按钮后的逻辑
                String username = etUsername.getText().toString();
                String password = etPassword.getText().toString();
                // 调用登录接口进行登录操作
            }
        });

        tvRegister.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // 点击注册链接后的逻辑
                Intent intent = new Intent(LoginActivity.this, RegisterActivity.class);
                startActivity(intent);
            }
        });
    }
}

RegisterActivity.java

public class RegisterActivity extends AppCompatActivity {

    private EditText etUsername;
    private EditText etPassword;
    private EditText etConfirmPassword;
    private Button btnRegister;
    private TextView tvLogin;

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

        etUsername = findViewById(R.id.et_username);
        etPassword = findViewById(R.id.et_password);
        etConfirmPassword = findViewById(R.id.et_confirm_password);
        btnRegister = findViewById(R.id.btn_register);
        tvLogin = findViewById(R.id.tv_login);

        btnRegister.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // 点击注册按钮后的逻辑
                String username = etUsername.getText().toString();
                String password = etPassword.getText().toString();
                String confirmPassword = etConfirmPassword.getText().toString();
                // 调用注册接口进行注册操作
            }
        });

        tvLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // 点击登录链接后的逻辑
                Intent intent = new Intent(RegisterActivity.this, LoginActivity.class);
                startActivity(intent);
            }
        });
    }
}

以上代码仅为一个基本框架，具体的实现需要根据自己的需求进行修改。需要注意的是，登录注册涉及到用户敏感信息，需要进行加密传输和存储，同时也需要进行错误处理和异常处理。