Code Conventions for the Java Programming Language(Java语言编码规范英文版)

6 - Declarations

6.1 Number Per Line

One declaration per line is recommended since it encourages commenting. In other words,

int level; // indentation level
int size;  // size of table

is preferred over

int level, size;

Do not put different types on the same line. Example:

 
		      int foo,  fooarray[]; //WRONG!

Note: The examples above use one space between the type and the identifier. Another acceptable alternative is to use tabs, e.g.:

int	level;	        // indentation level
int	size;	         // size of table
Object	currentEntry;	 // currently selected table entry

6.2 Initialization

Try to initialize local variables where they're declared. The only reason not to initialize a variable where it's declared is if the initial value depends on some computation occurring first.

6.3 Placement

Put declarations only at the beginning of blocks. (A block is any code surrounded by curly braces "{" and "}".) Don't wait to declare variables until their first use; it can confuse the unwary programmer and hamper code portability within the scope.

void myMethod() {
    int int1 = 0;         // beginning of method block

    if (condition) {
        int int2 = 0;     // beginning of "if" block
        ...
    }
}

The one exception to the rule is indexes of for loops, which in Java can be declared in the for statement:

for (int i = 0; i < maxLoops; i++) { ... }

Avoid local declarations that hide declarations at higher levels. For example, do not declare the same variable name in an inner block:

int count;
...
myMethod() {
    if (condition) {
        int count = 0;     // AVOID!
        ...
    }
    ...
}

6.4 Class and Interface Declarations

When coding Java classes and interfaces, the following formatting rules should be followed:

No space between a method name and the parenthesis "(" starting its parameter list
Open brace "{" appears at the end of the same line as the declaration statement
Closing brace "}" starts a line by itself indented to match its corresponding opening statement, except when it is a null statement the "}" should appear immediately after the "{"

class Sample extends Object {
    int ivar1;
    int ivar2;

    Sample(int i, int j) {
        ivar1 = i;
        ivar2 = j;
    }

    int emptyMethod() {}

    ...
}

Methods are separated by a blank line

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