How to convert Integer to int?

问题

I am working on a web application in which data will be transfer between client & server side.

I already know that JavaScript int != Java int. Because, Java int cannot be null, right. Now this is the problem I am facing.

I changed my Java int variables into Integer.

public void aouEmployee(Employee employee) throws SQLException, ClassNotFoundException
{
   Integer tempID = employee.getId();
   String tname = employee.getName();
   Integer tage = employee.getAge();
   String tdept = employee.getDept();
   PreparedStatement pstmt;
   Class.forName("com.mysql.jdbc.Driver");
   String url ="jdbc:mysql://localhost:3306/general";
   java.sql.Connection con = DriverManager.getConnection(url,"root", "1234");
   System.out.println("URL: " + url);
   System.out.println("Connection: " + con);
   pstmt = (PreparedStatement) con.prepareStatement("REPLACE INTO PERSON SET ID=?, NAME=?, AGE=?, DEPT=?");
   pstmt.setInt(1, tempID);
   pstmt.setString(2, tname);
   pstmt.setInt(3, tage);
   pstmt.setString(4, tdept);
   pstmt.executeUpdate();
 }

My problem is here:

pstmt.setInt(1, tempID);

pstmt.setInt(3, tage);

I cant use the Integer variables here. I tried with intgerObject.intValue(); But it makes things more complex. Do we have any other conversion methods or conversion techniques?

Any fix would be better.

回答1:

As already written elsewhere:

For Java 1.5 and later you don't need to do (almost) anything, it's done by the compiler.
For Java 1.4 and before, use Integer.intValue() to convert from Integer to int.

BUT as you wrote, an Integer can be null, so it's wise to check that before trying to convert to int (or risk getting a NullPointerException).

pstmt.setInt(1, (tempID != null ? tempID : 0));  // Java 1.5 or later

pstmt.setInt(1, (tempID != null ? tempID.intValue() : 0));  // any version, no autoboxing

^*using a default of zero, could also do nothing, show a warning or ...

I mostly prefer not using autoboxing (second sample line) so it's clear what I want to do.

回答2:

Since you say you're using Java 5, you can use setInt with an Integer due to autounboxing: pstmt.setInt(1, tempID) should work just fine. In earlier versions of Java, you would have had to call .intValue() yourself.

The opposite works as well... assigning an int to an Integer will automatically cause the int to be autoboxed using Integer.valueOf(int).

回答3:

Java converts Integer to int and back automatically (unless you are still with Java 1.4).

回答4:

Another simple way would be:

Integer i = new Integer("10");

if (i != null)
    int ip = Integer.parseInt(i.toString());

回答5:

Perhaps you have the compiler settings for your IDE set to Java 1.4 mode even if you are using a Java 5 JDK? Otherwise I agree with the other people who already mentioned autoboxing/unboxing.

来源：https://stackoverflow.com/questions/3571352/how-to-convert-integer-to-int

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