Html-margin , border, padding

margin: 元件本身和其他元件之間的空間
border: 填滿元件本身的邊界
padding: 填滿元件內容到元件邊界之間的空間.

CSS line-height usage

This property can align the text within a input tag

 

     style='left: 210; top: 22; width: 110; line-height: 54px; height: 54; font-size: 36;' />
 

Java Static Variable

public class StaticVariableTest {
 
 public static void main(String []args){
  Student s1 = new Student();
  Student.height =1;
  Student s2 = new Student();
  Student.height =2;
  System.out.println(Student.height);
 }

}

class Student{
 static int height;
}

Java ArrayList

public class ArrayListDemo {

 public static void main(String[] args) {
  /**
   * Following example will cause a run time exception:
   * java.lang.ClassCastException, although no compilation error happened.
   */
  
  /*
   * int sum = 0; 
   * ArrayList al = new ArrayList(); 
   * al.add("1"); 
   * al.add(new Integer(2));
   *  for (int i = 0; i < al.size(); i++) { 
   *  sum+= (Integer)al.get(i); 
   *  } 
   *  System.out.println(sum);
   */

  /**
   * Following example will fix above problem.
   */
  int sum = 0;
  ArrayList al = new ArrayList();
  // al.add("1"); this line has a compilation error.
  al.add(new Integer(1));
  al.add(new Integer(2));
  for (int i = 0; i < al.size(); i++) {
   sum += (Integer) al.get(i);
  }
  System.out.println(sum);
 }

}

Merge Sort (合併排序法)

package sort;

public class MergeSortDemo {
 
 
 public static void main(String[] args) {
  int[] array = { 3, 3,2,1,0,4,5,1,4};
  array = mergeSort(array);
  for (int i = 0; i < array.length; i++) {
   System.out.print(array[i] + " ");
  }
 }

 public static int[] mergeSort(int[] list) {
  //if merely left 1 element return list;
  if (list.length <= 1) {
   return list;
  } else {
   int[] left;
   int[] right;
   int middle = list.length / 2;
   //declare left sub array;
   left = new int[middle]; 
   //declare right sub array;
   right = new int[list.length - middle];
   int j = 0;
   for (int i = 0; i < list.length; i++) {
    if (i < left.length) {
     //initialize left array
     left[i] = list[i];
    } else {
     //initialize right array
     right[j] = list[i];
     j++;
    }
   }
   //divide left array into small parts;
   left = mergeSort(left);
   //divide right array into small parts;
   right = mergeSort(right);
   //combine small parts of left and right 
   return merge(left, right);
  }
 }

 public static int[] merge(int[] left, int[] right) {
  int[] result = new int[left.length + right.length];
  int j = 0;
  while (left.length > 0 || right.length > 0) {
   //left and right array have elements.
   if (left.length > 0 && right.length > 0) {
    if (left[0] <= right[0]) {
     result[j] = left[0];
     left = shiftArray(left);
    } else {
     result[j] = right[0];
     right = shiftArray(right);
    }
    
   } else if (left.length > 0) {
    //left array has elements;
    result[j] = left[0];
    left = shiftArray(left);
   } else if (right.length > 0) {
    //right array has elements;
    result[j] = right[0];
    right = shiftArray(right);
   }
   j++;
  }
  return result;
 }

 private static int[] shiftArray(int[] i) {
  int[] result = new int[i.length - 1];
  for (int j = 0; j < result.length; j++) {
   result[j] = i[j+1];
  }
  return result;
 }
}

Reference Wiki

Recursive Selection Sort (遞迴選擇排序法)

維護舊有Java程式專案

1:  public class RecursiveSelectionSort {  
2:      public static void main(String[] args) {  
3:          int [] array ={5,2,3,6,1,7,0,9,100,4,8};  
4:          selectionSort(array, array.length);  
5:          for(int i=0;i<array.length;i++){  
6:              System.out.print(array[i]+" ");  
7:          }  
8:      }  
9:      /**  
10:       * Using the concept of selection sort.  
11:       * Implemented by an iterative and a recursive mechanisms.  
12:       *   
13:       * Following are steps:  
14:       * 1.Finding the smallest one and its index;  
15:       * 2.Put the smallest into the right end side;  
16:       * 3.Decrease the array size;  
17:       * Recursively calling this method.  
18:       *   
19:       * @param array unsorted array  
20:       * @param length array length  
21:       */  
22:      public static void selectionSort(int[] array , int length) {  
23:          if(length > 0){  
24:              int smallestIdx = 0 ;  
25:              int smallest = array[smallestIdx];  
26:              //1.From left to right find the smallest one and its index;  
27:              for(int i =0 ;i<length ;i++){  
28:                  if(array[i]< smallest){  
29:                      smallest = array[i];  
30:                      smallestIdx = i;  
31:                  }  
32:              }  
33:              //2.Put the smallest into the right end side;  
34:              swapElements(array,smallestIdx,length -1);  
35:              //3.Decrease the array size;  
36:              length -=1;  
37:              //4.Recursively calling this method.  
38:              selectionSort(array,length);  
39:          }  
40:      }  
41:      private static void swapElements(int[] array, int idx, int idx1) {  
42:          int tmp = array[idx];  
43:          array[idx] = array[idx1];  
44:          array[idx1] = tmp;  
45:      }  
46:  }  

一中兩區

一中兩區?? 統一不是壞事, 如果跟民主國家統一那沒問題,

要跟共產國家統一??請舉辦公投,如果通過的話,就統一好了,

再這樣下去,會真的成為馬區長.!!

最好是維持現狀,等待中國成為民主國家再說

Binary Search (Recursive version)

Before you do binary search, you should sort the unsorted elements first 在使用binary搜尋之前, 要先把資料排序過. Sort(排序)

public class BinarySearch {
 
 public static void main(String [] args){
  int [] i ={2,3,4,4,5,6,7,87};
  System.out.println(binarySearch(i,0,i.length-1,5));
  
 }
 
 public static int binarySearch(int[] i, int left, int right, int target) {
  int middle = (left+right)/2;
  if (i[middle] == target) {
   return middle;
  } else if (i[middle] > target) {
   return binarySearch(i,left,middle,target);
  } else{
   return binarySearch(i,middle,right,target);
  }
 }
}

A c++ binary search tree

Iterative and Recursive

Java Inner Class(內部類別)

public class InnerClassDemo {

 class Student{
  void print(){
   System.out.println("This is an inner class as an instance variable");
  }
 }
 
 void classInAmethod(){
  class Son{
   void print(){
    System.out.println("I am within a method");
   }
  }
  Son s = new Son();
  s.print();
 }
 
 public static void main(String[]args){
  InnerClassDemo is = new InnerClassDemo();
  is.classInAmethod();
  InnerClassDemo.Student s = is.new Student();
  s.print();
 }

}

資料來源:http://docs.oracle.com/javase/tutorial/java/javaOO/innerclasses.html
相關文章:anonymous class

你真的是一個programmer嗎??

光會if-else, for or while loop, call 3rd party library, or 知道常用的framework, 對於programmer 來說, 以上只是必須的基本技巧, 嚴格來說要能實做出各種演算法,才能說自己會寫程式.

Java 變數指定

import java.util.ArrayList;

public class VariableAssignDemo {

 public static void main(String[] args){
  ArrayList a1 = new ArrayList();
  a1.add(1);
  /**
   * Following case assigns object reference to a new variable
   */
  ArrayList a2 =a1;
  a2.add(2);
  System.out.println(a1.toString());
  System.out.println(a2.toString());
  
  System.out.println("-------------------");
  
  /**
   * Following is a deep copy , all elements are included..
   * If you want to keep original object , but do some changes on it.
   * A deep copy is a solution.
   */
  ArrayList a4 =new ArrayList();
  for(int i = 0 ;i < a1.size() ;i++){
   a4.add(a1.get(i));
  }
  a1.remove(0);
  System.out.println(a1.toString());
  System.out.println(a4.toString());
  
 }
}

Java method override

public class OverwriteDemo {

}

class Father{
 
 void print(){
  
 }
}

class Son extends Father{
 
 //  compile-error
 // private void print(){
 // }
 
 protected void print(){
  
 }
}

Java Properties

 import java.io.*;  
 import java.util.Properties;  
 public class PropertiesDemo {  
     /**  
      * File Name: some.prop  
      * Content : msg= Hello World.  
      */  
     public static void main(String[] args) throws IOException {  
         // First you must create a file named "some.prop" then choose it .  
         FileInputStream fis = new FileInputStream("some.prop");  
         Properties prop = new Properties();  
         prop.load(fis); // Load properties from file input stream  
         String meesage = (String) prop.get("msg"); // get entry key  
         System.out.println(meesage);// print it out  
         prop.setProperty("msg", "modified Hello World");// add or modify new properties.  
         FileOutputStream fos = new FileOutputStream("some.prop");// Get property source file again.  
         prop.store(fos, "modified propery file");// Save the newest contents into the property file  
         prop.list(System.out);// List them out.  
     }  
 }  

相關連結:
http://goodideascome.blogspot.com/2011/12/spring-ioc-with-hello-world-example.html

Java exception -例外處理

Runtime exception: 非程式設計師所能預期到的錯誤.可直接拋出.

如果類似檔案找不到 ,這種可預期的錯誤狀況便要利用

try ..catch 把錯誤接收起來並做適當的處理

import java.io.*; 
public class ExceptionDemo { 
     public static void main(String[] args) throws FileNotFoundException{ 
          int i =Integer.parseInt("r"); // this is a runtime exception 
          System.out.println(i); 
          //using a try catch block to catch checked exception 
          try { 
               FileReader fr = new FileReader(new File("xxx.txt")); 
          } catch (FileNotFoundException e) { 
               // TODO Auto-generated catch block 
               e.printStackTrace(); 
          } 
          //or throw out this exception to the caller. 
          FileReader fr = new FileReader(new File("xxx.txt")); 
     } 
} 

Following is a fail case.

public class UnreachableDemo {
 public static void main(String[] args){
  int [] k =new int []{1,2,3};
  for(int i = 0 ; i < k.length+1 ; i++ ){
   System.out.println(k[i]);
  }
  System.out.println("arrive here?");
 }
}

Following is a success case.

public class ReachableDemo {
 public static void main(String[] args){
  int [] k =new int []{1,2,3};
  try{
   for(int i = 0 ; i < k.length+1 ; i++ ){
    System.out.println(k[i]);
   }
   System.out.println("within a try block , so it is unreachable");
  }catch(Exception e){
   e.printStackTrace();
  }
  System.out.println("outside");
 }
}

Java action listener

Inner Class implementation:



Change getHelloButton with follwing example, you will get an anonymous version implementation:

Java 物件比較

因為底下這兩個物件都有相同的記憶體位址,所以都是true.

如果equals方法,有被覆寫過的話,那麼hashCode方法也需要被覆寫, 以確保物件的相同.


Java 物件equals method 的用法

什麼是unicode?

unicode是一種字元編碼的方式,
每一個字元無論在哪一種作業系統平台,或程式語言都只有一個唯一utf的號碼.

下面這個例子是寫入中文, 然後用英文編碼讀取, 所以會讀出亂碼.


若寫入和讀出都是使用unicode的話,就可以正常顯示.

JSP 標籤函式庫

uri :此函式庫的位址.

prefix : 如果有引用很多tag library的話,可以用來區別各個不同的函式庫的名稱.

參考文章:http://java.sun.com/products/jsp/tutorial/TagLibraries5.html

SCWCD 考試目標 :JSP技術-1

被包覆在out.println()可列印出來的部分,還有網頁本身的文字都算是template text.



scripting elements (comments, directives, declarations, scriptlets, and expressions)

comments: 註解


directives: 指令,jsp有三種指令: page , include , taglib


declarations: 變數宣告


scriptlet: 一般Java的程式碼


expressions: 描述

Java Thread join 用法

Java thread(執行緒)

Java 物件轉型

Animal ani = new Dog();
隱性轉型,此時的ani變數只可使用Animal類別提供的方法,
無法使用Dog類別的方法.
(可以大容器裝小物件)

Dog dg1 = new Animal();
(小容器裝大物件,會產生編譯錯誤)

Dog dg2 = (Dog)ani;
明確轉型,此時我們指定animal就是dog.
這是多型的用法,假如有一個cat類別也繼承animal,
也可轉型為cat來使用.

如果不確定執行時期的物件是哪一個類別的實體,

可以使用instanceOf這個方法來判斷,以避免丟出

exception





本文參考網址
http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html

Java 字元編碼轉換

native2ascii 欲轉換的中文字

會印出unicode版本的資源編碼.

Java Serialization (Java 序列化)

一般來說物件實體只能存活在JVM中如果想要把物件的實體狀態給保留下來的話,可以使用序列化這個技術,以下是把物件實體寫入檔案的例子.

而SerializationReadSample.java則是把剛剛序列化後的物件,讀回來的程式碼:


只要欲保存的類別有implement Serializable這個界面, 就可以拿來作序列化的動作.

當類別中有不想被序列化的field, 例如,socket, or thread等等的動態內容,

則可以在宣告變數的時候加上transient 這個關鍵字.


千萬不可序列化內部類別(inner class) , 無論是local或是匿名內部類別. 因為這麼做的話 ,

compiler會為內部類別產生合成的建構子.  因為合成的建構子 , 在source code找不到實作的細節

會隨著java compiler版本的不同, 而產生不同的建構子, 也就是說你在A版本編譯出來的code,

很可能在B版本跑不起來 , 造成相容性的問題 .

容錯(Fail-over support)和負載平衡(Load Balancing)

容錯: 當一台server無法服務客戶端的請求時, 其他的server可以立刻把所有的服務請求接收過來執行.

負載平衡: server會把客戶端請求,分配給目前工作loading較不重的server來執行.