如何找出可在大量Android手机上安全使用的Java最低版本？

Question

I recently found out at work we're limiting our Java target to 1.1, because there are supposedly still Android phones that only support up to that version. I've been trying to Google which versions of Java are installed on the different version of Android (unless they do get updated, then what is the minimum version that's included?), and have had no such luck in my search.

So, I'm trying to find out what is realistically the best minimum target for Java on Android. Know of any good sources detailing the versions of Java used across Android devices?

[Edit] For clarification, we're using the Java SDK to build a jar, then packaging it into the apk. So I do need to know a specific Java SDK target, not the Android API level.

Answer 1

You can support all major versions of Android (2.1 and above, possibly even lower) with Java 1.6.

Infact, as long as you compile with anything but 1.7 you'll be fine, though compiling with 1.5 and below gives a bunch of errors with @Override annotations. 1.6 is your safest bet. I've used it in all my apps so far, and haven't found a single device that was incompatible because of my Java version.

Answer 2

First don't confuse Java with Android. The Java-RE and the Android system itself are different.

If you talk about Android versions, you should support API level 8 at a minimum and target API level 17. That should give your access to 90% and more of all Android devices.

The rest Raghav already wrote.

For Java as a compiler itself: You can use JavaSDK 7 without any issue but you shouldn't use a compile setting above 1.6. Using 1.1 is way outdated!

Answer 3

Update: It's nowadays Java 7 without try-with-resource and without some newer methods & classes. Your IDE will complain if you use something you shouldn't.

The Android tools know Java 7 and are capable of transforming it into Android bytecode that runs on old devices.

One can also use the full set of Java 7 features (ie including try-with-resources) for apps targeting Android 4.4 and up.

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Downloading and Building Android itself requires

JDK 6 if you wish to build Gingerbread or newer; JDK 5 for Froyo or older.

Building older versions with JDK 6 works in my experience since the class format generated by the Java compiler is still compatible with the class format of JDK 5.

The same applies to Apps. Android's internal Java implementation is not the same as the JDK so it has no comparable version numbers. But for example String#isEmpty() that was added in JDK 6 says Added in API level 9 in Android's documentation which is exactly the version after aforementioned Froyo.

Eclipse / Android Lint will also mark usage of those methods as error if your App has a lower minimum version than 9.

Using JDK 6 to build any app should work perfectly fine. Your code must not use core Java methods that did not exist on older Android versions just like any other method in the Android framework. It is also no problem to use @Override annotations for implemented interfaces since that annotation is not included in the .class file (see RetentionPolicy.SOURCE ).

What actually matters in the end is that Android's dex compiler that turns all the .class files into an Android .dex file actually understands the class format and can produce a valid dex file. The dex format is the one has to be understood by whatever old Android phone you have and I'd assume that the dex compiler makes sure that it produces a valid format for any version of Android. (Here is AFAIK the problem with JDK 7 since the class format has changed)

I'd suggest that you use Java 6 as compile target to build any of your apps. That results in the most recent version of .class file that the dex compiler understands. Older versions do work but you might get warnings like the following

[dx] warning: Ignoring InnerClasses attribute for an anonymous inner class
[dx] (com.bubblesoft.org.apache.commons.logging.impl.LogFactoryImpl$1) that doesn't come with an
[dx] associated EnclosingMethod attribute. This class was probably produced by a
[dx] compiler that did not target the modern .class file format. The recommended
[dx] solution is to recompile the class from source, using an up-to-date compiler
[dx] and without specifying any "-target" type options. The consequence of ignoring
[dx] this warning is that reflective operations on this class will incorrectly
[dx] indicate that it is *not* an inner class.