在这种情况下如何返回true或false？

Question

Here is a my code

   public boolean changePassword(String password, String id) {

    try {

        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
        StrictMode.setThreadPolicy(policy);

        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection(DB_URL, DBuser, DBpassword);


        Statement st = conn.createStatement();
        String updateQuery = "update teacher_registration set password="+password+"where teacher_id="+id;
        ResultSet rs = st.executeQuery(updateQuery);

        if(rs!=null){
            return true;
        }else{
            return false;
        }
    } catch (Exception e) {
        e.printStackTrace();
    }

}

I want to return true if rs is not null else return false.

But i am getting an error at the closing bracket of this method. It is asking me to return a true or false again even if I did so in the try catch block earlier.

This is my first time working with java.

Please HELP!

Answer 1

Do something like this

public boolean changePassword(String password, String id) {
  boolean result = false;

try {

    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
    StrictMode.setThreadPolicy(policy);

    Class.forName("com.mysql.jdbc.Driver");
    Connection conn = DriverManager.getConnection(DB_URL, DBuser, DBpassword);


    Statement st = conn.createStatement();
    String updateQuery = "update teacher_registration set password="+password+"where teacher_id="+id;
    ResultSet rs = st.executeQuery(updateQuery);

    if(rs!=null){
        result = true;
    }else{
        result = false;
    }
} catch (Exception e) {
    e.printStackTrace();
}
 return result;
}

Answer 2

Your mistake is you return the value in the try block. If something fails, you won't return anything. Try moving the return statement outside the try block or add a return false; after the catch block.

Answer 3

I think update query pieces don't combine together well.

In this case 'where' become a part of your password (at the end).

Try this:

String updateQuery = "update teacher_registration set password="+password+" where teacher_id="+id;

Plus you can move your condition into catch block or do even better as show below.

Full version of your code:

public boolean changePassword(String password, String id) {

    try {

        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
        StrictMode.setThreadPolicy(policy);

        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection(DB_URL, DBuser, DBpassword);


        Statement st = conn.createStatement();
        String updateQuery = "update teacher_registration set password="+password+" where teacher_id="+id;
        ResultSet rs = st.executeQuery(updateQuery);
        if(rs!=null){
            return true;
        }

    } catch (Exception e) {
        e.printStackTrace();
        return false;
    }

}

Answer 4

If there is an exception generated in your try block, your return statements will not be reached. After catching the exception, you simply need to return a value. I assume that you return true if the change is successful, so return false if there is an exception.

try{
    // Your code
} catch (Exception e) {
    e.printStackTrace();
}
return false;