Java Fragmentation Knowledge

1. There is a goto in Java, but this is only a reserved word and cannot be used (const is also). The error message in Eclipse is "Syntax error on token" goto ", throw expected".

A similar function of Goto is implemented by the break/continue tag.

(1) Break label

outer:          for (int i=0; i<10; i++) {            if(i = =5                )break  outer            ; + " ");        }

Results: 0 1 2 3 4

Analysis: Break jumps through the tag to the For loop body, and then no longer enters the loop.

(2) Continue label

outer:          for (int i=0; i<3; i++) {            for (int j=11; j<15; j + +) {                if (j = =)                    continue  outer;                 + "" + j + "");            }        }

Results: 0 11 0 12 1 11 1 12 2 11 2 12

Analysis: Continue jumps to the for outside through the tag, but just jumps out of the current loop and it re-enters the for loop.

2. Can I access non- static variables in the static environment ?

Eclipse Tip: Cannot make a static reference to the Non-static field

3. Identifiers and Unicode

Identifiers can consist of letters (Unicode), numbers, currency symbols (￥,$), and connection symbols (_).

This concerns Unicode, and not all Unicode can be used as part of an identifier. Also, not only numbers cannot be the first character of an identifier.

intStart = 0; intPart = 0;  for(inti=0x0000; i<=0x10ffff; i++) {            if(Character.isjavaidentifierstart (i)) {start++;//System.out.println (Character.tochars (i));            }            if(Character.isjavaidentifierpart (i)) part++; } System.out.println ("Number of Unicode character sets:" + (0x10ffff+1)); System.out.println ("As the number of first characters:" +start); System.out.println ("As part of the identifier:" +Part ); System.out.println ("Difference between the two:" + (Part-start));

Results:

4.i++ and ++i

This is not just the first plus and after add how simple, for i++, actually I is the value of the first copy to a temporary variable, and then add 1 (like ++i), and finally participate in the operation.

int i = 1;         = i++;        System.out.println (i);

Results: 1

The implementation of the i++ is as follows:

    int temp = i;    i = i+1;    return temp;

What is the result of 5.i+++j?

        int i = 1, j = 3, result;         = i+++J;        System.out.println ("Result:" + result);        System.out.println ("i =" + i);        System.out.println ("j =" + j);    

Results:

Analysis: Equivalent to (i++) +j. The compiler takes greedy rules and tries to find as many operators as possible (if you learn how the compilation principle can understand why).

　　

Java Fragmentation Knowledge