The main rule: a variable must be declared before it is used. If you do this later, the program simply will not work.
System.out.print(greeting);
greeting = "Father!";
The launch of the program the above ends with an error:
Error: java: cannot find symbol
symbol: variable greeting
This error means that the code uses a variable that is not defined. And in the error itself they say this directly: variable greeting. In addition to the wrong order of definition, in Java there are commonplace typos, both when using a variable and when it is declared.
The number of such errors is reduced by using a properly configured editor. This editor highlights the names that are used without the announcement and warns of possible problems.
Find an undeclared variable in the program and declare it assigning to it the value of "Dragon"
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If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:
Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.
It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.
In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.
It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.
By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.