The syntax is a [...]]]> JDK 7 has several enhancements to the try-catch construct. Try with resources allows for ensuring that resources are closed and freed up without the need to explicitly call the close function. Any class implementing java.lang.AutoCloseable can be automatically closed without the need for a finally section in the try block.

The syntax is a try with parens and the resources to automatically close out inside the parens.
try ( resources ) { code } catch (exception) { }

snippet 1 shows the syntax for try with resources:

try (
    BufferedReader reader = new BufferedReader(
        new FileReader("c:/dev/jdk7test/t1.ofx"));
   BufferedWriter writer = new BufferedWriter(
        new FileWriter("c:/dev/jdk7test/output.txt"))
   ) {
         // read and write
     }

Another change to try is that the catch can now handle multiple exception types in one block. Multiple catch blocks are optional and still work fine if you prefer to separate the handling. Just separate the exception types with | .

Snippet 2 catch with multiple exception types:

catch (java.io.FileNotFoundException | java.io.IOException ex) {
    System.out.println(ex.getMessage());
}

Lastly here is a small simple class that shows both features in action.

package jdk7test;
import java.io.*;
public class Jdk7TryWithResourcesTest {
    public static void main(String[] args) {
        Jdk7TryWithResourcesTest test = new Jdk7TryWithResourcesTest();
        test.execute();
    }

    public void execute() {
        try (
                BufferedReader reader = new BufferedReader(new FileReader("c:/dev/jdk7test/t1.ofx"));
                BufferedWriter writer = new BufferedWriter(new FileWriter("c:/dev/jdk7test/output.txt"))
            ) {
            String line;
            while ((line = reader.readLine()) != null){
                writer.write(line);
            }
        } catch (java.io.FileNotFoundException | java.io.IOException ex) {
            System.out.println(ex.getMessage());
        }
    }
}

At the bottom of this post is a small [...]]]> JDK 7 adds the ability to use String objects as the case in switch blocks. It’s not exactly an earth shattering addition but I find it quite useful in avoiding long if-then chains. Plus the release docs claim that using a switch is more efficient.

At the bottom of this post is a small java class that provides a complete example of use. Here is the part we’re concerned about. The switch takes a String argument that should be the abbreviated name of a month and sets the return value to the quarter of the year that month is in.

switch(monthIn) {
            case "Jan":
            case "Feb":
            case "Mar":
                retval = "Q1";
                break;
            case "Apr":
            case "May":
            case "Jun":
                retval = "Q2";
                break;
            case "Jul":
            case "Aug":
            case "Sep":
                retval = "Q3";
                break;
            case "Oct":
            case "Nov":
            case "Dec":
                retval = "Q4";
                break;
            default:
                throw new IllegalArgumentException("Invalid Month argument: " + monthIn);
}

That’s a pretty geedunk example but it shows the functionality and is simple to read/understand. Here is a complete class that shows the same switch statement in use:

package jdk7test;
import java.util.Calendar;

public class Jdk7test {
    public static void main(String args[]) {
        Jdk7test test = new Jdk7test();
        test.execute();
    }

    public void execute() {
        String[] strMonths = new String[] { "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug",
                                            "Sep", "Oct", "Nov", "Dec" };
        Calendar cal = Calendar.getInstance();
        try {
            String monthName = strMonths[cal.get(Calendar.MONTH)];
            String quarter = getQuarter(monthName);
            System.out.println("Month: " +  monthName + " is in quarter: "
                               + quarter);
        } catch (IllegalArgumentException e) {
            System.out.println("The month sent to getQuarter was invalid");
            System.out.println(e.getMessage());
        }
    }

    public String getQuarter(String monthIn) {
        String retval;
        switch(monthIn) {
            case "Jan":
            case "Feb":
            case "Mar":
                retval = "Q1";
                break;
            case "Apr":
            case "May":
            case "Jun":
                retval = "Q2";
                break;
            case "Jul":
            case "Aug":
            case "Sep":
                retval = "Q3";
                break;
            case "Oct":
            case "Nov":
            case "Dec":
                retval = "Q4";
                break;
            default:
                throw new IllegalArgumentException("Invalid Month argument: " + monthIn);
        }
        return retval;
    }
}

As I test out the release I’ll do some posts on [...]]]> Build 147 for JDK 7 is now available with the goal of a generally available release later this month. Some good resources are:

• Oracle’s Java 7 wiki
• Java 7 project page
• Get the release from the download page
• Oracle’s Java SE 7 documentation

As I test out the release I’ll do some posts on new features.

Java, Java 7, JDK 7, Roger Cuddy