Java – Tianyu's notes

can’t find Java desktop application troubleshoot

guoty3310 — Wed, 23 Oct 2013 03:38:44 +0000

Support for [B]SAF (JSR 296, basically the framework that was behind your “Java Desktop Application” project template) has been abruptly dropped (for no valid reason, let me add).

However, as Bill says in his answer, it is not necessary to use the SAF in order to visually design a form. NetBeans swing-designer (known as Matisse) can be used to design any JFrame, JDialog, JPanel, etc.

You just have to

Right click -> New -> JFrame Form...

and you’re ready to drag-and-drop!

(The features you’ll be missing are the extra bells and whistles that such framework provided, like SAF Actions, windowing persistence, simplified management for long running Tasks and related visual feedback [now you have to get your hands dirty with the SwingWorker class], etc)

From

stackoverflow.com/questions/9146976/why-cant-i-find-java-desktop-application-in-netbeans-7-1

what is constructor in java

guoty3310 — Tue, 16 Jul 2013 20:59:39 +0000

Length (Photo credit: Wikipedia)

constructor, which is similar to a method but is used only at the time an object is created to initialize the object’s data.

用new给一个类创建对象的时候会自动调用该类的构造函数，给对象赋初值等；method是普通的方法，需要在时才调用它。

java构造函数

一般我们讲的“函数”就是“方法”；
构造函数=构造方法；
构造方法是一种特殊的方法，具有以下特点。
（1）构造方法的方法名必须与类名相同。
（2）构造方法没有返回类型，也不能定义为void，在方法名前面不声明方法类型。
（3）构造方法的主要作用是完成对象的初始化工作，它能够把定义对象时的参数传给对象的域。
（4）一个类可以定义多个构造方法，如果在定义类时没有定义构造方法，则编译系统会自动插入一个无参数的默认构造器，这个构造器不执行任何代码。
（5）构造方法可以重载，以参数的个数，类型，或排列顺序区分。

class RectConstructor{
double length;
double width;
double area(){
return length*width;
}
RectConstructor(double width,double length){//带参数的构造方法
this.length=length;
this.width=width;
}
}
public class RectDemo{
public static void main(String args[]) {
RectConstructor rect1=new RectConstructor(10,20);
RectConstructor rect2=new RectConstructor(3,6);
double ar;
ar=rect1.area();
System.out.println(“第一个长方形的面积是”+ar);
ar=rect2.area();
System.out.println(“第二个长方形的面积是”+ar);
}
}
控制台输出结果为：
第一个长方形的面积是200
第二个长方形的面积是18

what’s [\\s]?foo –Predefined Character & Quantifiers

guoty3310 — Thu, 11 Jul 2013 19:22:02 +0000

Predefined Character Classes

Construct	Description
`.`	Any character (may or may not match line terminators)
`\d`	A digit: `[0-9]`
`\D`	A non-digit: `[^0-9]`
`\s`	A whitespace character: `[ \t\n\x0B\f\r]`
`\S`	A non-whitespace character: `[^\s]`
`\w`	A word character: `[a-zA-Z_0-9]`
`\W`	A non-word character: `[^\w]`

private final String REGEX = "\\d"; // a single digit

In this example \d is the regular expression; the extra backslash is required for the code to compile. The test harness reads the expressions directly from the Console, however, so the extra backslash is unnecessary

Quantifiers

Greedy	Reluctant	Possessive	Meaning
`X?`	`X??`	`X?+`	`X`, once or not at all
`X*`	`X*?`	`X*+`	`X`, zero or more times
`X+`	`X+?`	`X++`	`X`, one or more times
`X{n}`	`X{n}?`	`X{n}+`	`X`, exactly `n` times
`X{n,}`	`X{n,}?`	`X{n,}+`	`X`, at least `n` times
`X{n,m}`	`X{n,m}?`	`X{n,m}+`	`X`, at least `n` but not more than `m` times

Ex1:

Enter your regex: .
Enter input string to search: @
I found the text "@" starting at index 0 and ending at index 1.
Enter your regex: \W
Enter input string to search: a
No match found.
Enter your regex: \W
Enter input string to search: !
I found the text "!" starting at index 0 and ending at index 1.

Ex2:

Enter your regex: a?
Enter input string to search: aaaaa
I found the text "a" starting at index 0 and ending at index 1.
I found the text "a" starting at index 1 and ending at index 2.
I found the text "a" starting at index 2 and ending at index 3.
I found the text "a" starting at index 3 and ending at index 4.
I found the text "a" starting at index 4 and ending at index 5.
I found the text "" starting at index 5 and ending at index 5.

Enter your regex: a*
Enter input string to search: aaaaa
I found the text "aaaaa" starting at index 0 and ending at index 5.
I found the text "" starting at index 5 and ending at index 5.

Enter your regex: a+
Enter input string to search: aaaaa
I found the text "aaaaa" starting at index 0 and ending at index 5.

Ex3:

Enter your regex: .*foo  // greedy quantifier,normally we are using greedy
Enter input string to search: xfooxxxxxxfoo
I found the text "xfooxxxxxxfoo" starting at index 0 and ending at index 13.
Enter your regex: .*?foo  // reluctant quantifier
Enter input string to search: xfooxxxxxxfoo
I found the text "xfoo" starting at index 0 and ending at index 4.
I found the text "xxxxxxfoo" starting at index 4 and ending at index 13.
Enter your regex: .*+foo // possessive quantifier
Enter input string to search: xfooxxxxxxfoo
No match found.

see  http://docs.oracle.com/javase/tutorial/essential/regex/pre_char_classes.html

Java 与 C++中static的用法

guoty3310 — Thu, 11 Jul 2013 16:10:41 +0000

Java 建立一个static静态变量的method指这个method不需要创建一个此类的对象即可使用:

class Simple{
static void go(){ //这个语句就已经可以直接运行了，不需再创建对象
System.out.println(“Go…”);
}
}
public class Cal{
public static void main(String[] args){
Simple.go(); //调用一个静态(static)方法就是“类名.方法名”
}
}

C++里的static中文叫全局变量,就是在函数外面定义的变量

全局变量只要在一个文件中定义后，在其他需要使用的源文件中只要使用extern关键字，即可在该文件中使用，概括下就是：extern扩展全局变量的作用域

extern in#include “stdio.h”t g_c; //其他文件中定义的全局变量

static int g_a = 1; //静态全局变量限本文件中使用

void fun1()
{
g_a++;
printf(“g_a=%d,g_c=%d\n“,g_a,g_c);
}

int g_b = 2; //全局变量

void main()
{
fun1();
g_a++;
printf(“g_a=%d,g_b=%d,g_c=%d\n“,g_a,g_b,g_c);
getchar();
}