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Thinking in Java
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Most procedural languages have the concept of scope. This determines both the visibility and lifetime of the names defined within that scope. In C, C++, and Java, scope is determined by the placement of curly braces {}. So for example:

  int x = 12;
  // Only x available
    int q = 96;
    // Both x & q available
  // Only x available
  // q “out of scope”

A variable defined within a scope is available only to the end of that scope.

Any text after a ‘//’ to the end of a line is a comment.

Indentation makes Java code easier to read. Since Java is a free-form language, the extra spaces, tabs, and carriage returns do not affect the resulting program.

Note that you cannot do the following, even though it is legal in C and C++:

  int x = 12;
    int x = 96; // Illegal

The compiler will announce that the variable x has already been defined. Thus the C and C++ ability to “hide” a variable in a larger scope is not allowed, because the Java designers thought that it led to confusing programs.
Thinking in Java
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   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire