Help -> About, then look for the java.home value in the Properties tab.If it is not showing a jdk1.6.0_xx version, where xx >= 11, then at a minimum I would recommend downloading and installing the latest Java 6 update (currently jdk1.6.0_43). Update your ...\sqldeveloper\sqldeveloper\bin\sqldeveloper.conf file so the SetJavaHome line is
depending on whether you use the 64-bit or 32-bit version of SQL Developer. It would also be a good idea to upgrade to the latest production release of SQL Developer (3.2.20.09.87). If you wish, you may keep multiple versions of SQL Developer installed, each in it's own distinct directory. It is not necessary to remove a prior version.
SetJavaHome C:/Program Files/Java/jdk1.6.0_43 or SetJavaHome C:/Program Files (x86)/Java/jdk1.6.0_43