Difference between jdk 1.6 and jdk 1.7 As follows:
 
JDK 6
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JDK 6 was released as part of Java SE 6.
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JDK 6 was released on 11th December 2006.
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Project Mustang is the code name of JDK 6.
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There are twenty seven subversions of JDK 6.
-  The latest version is 1.6.0_30.
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The new features and enhancements introduced in JDK 6 are: Creation of additional classes in java.awt package.
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Extended support for internationalization.
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Improvements in javax.swing.
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Introduction of system tray capability.
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Introduction to new type of compilers and lot more.
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JDK 6 also includes enhancements in Debugging.
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Avoiding memory leaks.
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Security support.
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Scripting Language Support.
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JDBC 4.0 API.
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Java Compiler API.
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Pluggable Annotations.
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Native PKI, Java GSS, Kerberos and LDAP support.
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Integrated Web Services.
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Lot more enhancements.
  
JDK 7
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JDK 7 was released as part of Java SE 7.
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JDK 7 was released on 07th July 2011.
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Project Dolphin is the code name of JDK 7.
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There are two subversions of JDK 7.The latest version number is 1.7.0_02.
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The new features and enhancements introduced in JDK 7 are: Enhanced support for dynamically typed languages.
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Strict type checking verifier.
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Upgrading of class loader architecture.
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Updates in collections and concurrency.
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Locale enhancement.
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Support for Unicode 6.
- 0 and lot more.
-  JDK 7 also includes enhancements and improvements in I/O and Networking,
Security.
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Cryptography.
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Database Connectivity .
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Client.
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Web and Management.
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Strings in switch Statement.
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Type Inference for Generic Instance Creation.
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Multiple Exception Handling.
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Support for Dynamic Languages.
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Try with Resources.
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Java nio Package.
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Binary Literals, underscore in literals.
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Diamond Syntax.
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Automatic null Handling.