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

8 - White Space

Blank lines improve readability by setting off sections of code that are logically related.

Two blank lines should always be used in the following circumstances:

One blank line should always be used in the following circumstances:

Blank spaces should be used in the following circumstances:

       while (true) {
           ...
       }

Note that a blank space should not be used between a method name and its opening parenthesis. This helps to distinguish keywords from method calls.

A blank space should appear after commas in argument lists.
All binary operators except . should be separated from their operands by spaces. Blank spaces should never separate unary operators such as unary minus, increment ("++"), and decrement ("--") from their operands. Example:

    a += c + d;
    a = (a + b) / (c * d);
    
    while (d++ = s++) {
        n++;
    }
    printSize("size is " + foo + "\n");

The expressions in a for statement should be separated by blank spaces. Example:

    for (expr1; expr2; expr3)

    myMethod((byte) aNum, (Object) x);
    myMethod((int) (cp + 5), ((int) (i + 3)) 
                                  + 1);