Java Learning (20110810)

today, after discuss with Martin, learn with another way.
I start to use chinese material, videos and files, and then explain to Martin. See whether this way is faster.
———————-
identifier (标识符)
start with letter, underline, $
legal: userName, User_Name, _sys_value, $change
illegal: 2mail, room#, class (reserved)
———–print format – printf———–
package ch.allenstudy.newway01;
public class NameConvention {
public static void main(String[] args)
{
int i = 47;
System.out.printf(“%d\n”, i);
System.out.printf(“%x\n”, i);
System.out.printf(“%#x\n”, i);
System.out.printf(“%#X\n”, i);
}
}

In Eclipse, run it, hint that has error. Force to run it, got below:
————————
Exception in thread “main” java.lang.Error: Unresolved compilation problems:
The method printf(String, Object[]) in the type PrintStream is not applicable for the arguments (String, int)
The method printf(String, Object[]) in the type PrintStream is not applicable for the arguments (String, int)
The method printf(String, Object[]) in the type PrintStream is not applicable for the arguments (String, int)
The method printf(String, Object[]) in the type PrintStream is not applicable for the arguments (String, int)

at ch.allenstudy.newway01.NameConvention.main(NameConvention.java:7)
————————–
But in the video, everything works fine.
Finally find the solution:
In Eclipse, Window > Preferences > Java > Compiler. Change the “Compiler compliance level” from default “1.4″ to “6.0″.
Then no erros.
Result is as below:
———————
47
2f
0x2f
0X2F
———————

Special character reprensation:
backslash: \\
Backspace: \b
Carriage return: \r
Tab (Form feed): \t
New line: \n
Single quote: \’
=====================================
package ch.allenstudy.newway01;
public class TestPrintf {
public static void main(String[] args)
{
char ch1 = ‘中’;
char ch2 = ‘\u4e2d’;
System.out.printf(“%c %c\n”, ch1, ch2);
}
}
Result:
中 中
This means that: \u4e2d is an alternative representation of Chinese character 中.
=====================================
Diff type variable number scope

 A sample of force conversion:
—————–
package ch.allenstudy.newway01;

public class TestPrintf {
public static void main(String[] args)
{
byte b = 10;
int i = 6;
i = b;
//b = i; //error
b = (byte) i; //ok, force to convert to byte
float x;
//x = 10*0.2; //error, 10*0.2 is double type
x = 10*0.2f; //ok, “f” means float
System.out.printf(b+”, “+i+”, “+x);
}
}
Result:
10, 10, 2.0
========================
package ch.allenstudy.newway01;

public class TestPrintf {
public static void main(String[] args)
{
int i = -3;
int j = 11;
int k = i & j; //3: 00000011 取反 1111110１， 11: 00001011
System.out.printf(“%d\n”, k);
}
}
Result: 9
Why? 我们一起看看与操作
１１１１１１０１
００００１０１１
__________
００００１００１
Ｓｏ　ｒｅｓｕｌｔ　ｉｓ　９．