Common Mistakes
Forgetting to declare your variables.
Histo.java:21: cannot find symbol symbol : variable count location: class Histo count = new ArrayList<Integer>(10); ^
Not importing a class:
Histo.java:9: cannot find symbol symbol : class Scanner location: class Histo Scanner data = null; ^
Forgetting to use the new keyword to create an object.
Here’s an example of the error message that occurs when you forget to use the new keyword. Notice that the message is pretty unhelpful. Java thinks you are trying to call the Method Scanner, but there are two problems. First Scanner is not really a method it is a constructor.:
Histo.java:14: cannot find symbol symbol : method Scanner(java.io.File) location: class Histo data = Scanner(new File("test.dat"));
Forgetting a Semicolon:
Histo.java:19: ';' expected System.exit(0); ^
Forgetting to declare the kind of object in a container.:
Note: Histo.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details.