Groovy tries to be as natural as possible for Java developers. We've tried to follow the principle of least surprise when designing Groovy, particularly for developers learning Groovy who've come from a Java background.
Here we list all the major differences between Java and Groovy.
All these packages and classes are imported by default, i.e. you do not have to use an explicit
import statement to use them:
Here we list the common things you might trip over if you're a Java developer starting to use Groovy.
- == means equals on all types. In Java there's a wierd part of the syntax where == means equality for primitive types and == means identity for objects. Since we're using autoboxing this would be very confusing for Java developers (since x == 5 would be mostly false if x was 5 . So for simplicity == means equals() in Groovy. If you really need the identity, you can use the method "is" like foo.is(bar). This does not work on null, but you can still use == here: foo==null.
- in is a keyword. So don't use it as a variable name.
- When declaring array you can't write you need to write
- If you were used to write a for loop which looked like
in groovy you can use that too, but you can use only one count variable. Alternatives to this are
Many Groovy programmers eschew the use of semicolons as distracting and redundant (though others use them all the time - it's a matter of coding style). A situation that leads to difficulties is writing the above in Groovy as:
This will throw a
The issue here is that in this situation the newline is not a statement terminator so the following block is treated as a closure, passed as an argument to the
Thing constructor. Bizarre to many, but true. If you want to use instance initializers in this sort of way, it is effectively mandatory to have a semicolon:
This way the block following the initialized definition is clearly an instance initializer.
New features added to Groovy not available in Java
- GroovyMarkup and GPath support
- native support for regular expressions
iteration and powerful switch statement
- dynamic and static typing is supported - so you can omit the type declarations on methods, fields and variables
- you can embed expressions inside strings
- lots of new helper methods added to the JDK
- simpler syntax for writing
beans for both properties and adding event listeners
- safe navigationusing the ?. operator, e.g. "variable?.field" and "variable?.method()" - no more nested ifs to check for null clogging up your code