class expand2{
 //利用函數(shù)的方法進(jìn)行數(shù)組的擴(kuò)充
 public static void main(String[] args) {
 //定義一個小型的數(shù)組
 int[] a={1,2,3,5};
 //調(diào)用擴(kuò)容函數(shù)
 //a=expand2(a);
 //a=expand3(a);
 a=expand4(a);
 //測試是否擴(kuò)容完成，輸出此時數(shù)組a中的值
 for (int i=0;i<a.length;i++) {
 System.out.println("aaaa:"+a[i]);
 }
 }

 //擴(kuò)容函數(shù)，
 public static int[] expand2(int a[]){
 //定義一個新數(shù)組b，并為其賦值長度為數(shù)組a的二倍
 int b[] = new int[a.length*2];
 //將數(shù)組a的元素循環(huán)遍歷到數(shù)組b中
 for (int i=0;i<a.length;i++) {
 b[i] = a[i];
 }
 //返回擴(kuò)容后的數(shù)組b
 return b;
 }

 //數(shù)組擴(kuò)容方法3，利用系統(tǒng)函數(shù)arraycopy進(jìn)行擴(kuò)容
 public static int[] expand3(int a[]){
 int[] b = new int[a.length*2];
 //系統(tǒng)函數(shù)進(jìn)行擴(kuò)容，將a[]的值賦值到b[]中，共a.length個長度。
 //相當(dāng)于第19-21行
 System.arraycopy(a,0,b,0,a.length);
 return b;
 }
 
 //數(shù)組擴(kuò)容方法4，利用系統(tǒng)函數(shù)copy進(jìn)行擴(kuò)容
 public static int[] expand4(int a[]){
 //可以查看api文檔，java.util.Arrays.copyOf的詳細(xì)使用；
 return java.util.Arrays.copyOf(a,a.length*2);
 }
}

public class CountCharDemo {
 public static void main(String[] args) {
  char key = '字';
  String str = "統(tǒng)計一個字符在字符串中的所有位置";
  int[] count=count(str,key);
  System.out.println(Arrays.toString(count));//[4, 7]
 }
 public static int[] count(String str,char key){
  int[] count={};
  for(int i=0;i<str.length();i++){
   char c=str.charAt(i);
   if(c==key){
    //擴(kuò)展數(shù)組
    count=Arrays.copyOf(count, count.length+1);
    //添加序號i
    count[count.length-1]=i;
   }
  }
  return count;
 }
}

public abstract class AbstractStringBuilder {
 /** The value is used for character storage.*/
 char value[];
 /** The count is the number of characters used.*/
 int count;
 /** Returns the length (character count).*/
 public int length() {
  return count;
 }

 public AbstractStringBuilder append(String str) {
  if (str == null)
   str = "null";
  int len = str.length();
  if (len == 0)
   return this;
  int newCount = count + len;
  if (newCount > value.length)
   expandCapacity(newCount);
  str.getChars(0, len, value, count);
  count = newCount;
  return this;
 }

 /**
  * 自動實(shí)現(xiàn)Java數(shù)組擴(kuò)容
  */
 void expandCapacity(int minimumCapacity) {
  int newCapacity = (value.length + 1) * 2;
  if (newCapacity < 0) {
   newCapacity = Integer.MAX_VALUE;
  } else if (minimumCapacity > newCapacity) {
   newCapacity = minimumCapacity;
  }
  value = Arrays.copyOf(value, newCapacity);
 }
}

/** 字符串?dāng)?shù)組與String類的原理 */
public class CharArrayDemo {
 public static void main(String[] args) {
  /* Java 可以將char[]作為字符串處理 */
  char[] ch1={'中','國','北','京'};
  char[] ch2={'歡','迎','您'};
  System.out.println(ch1);//中國北京
  System.out.println(ch2);//歡迎您
  /* char[]運(yùn)算需要編程處理,如連接: */
  char[] ch3=Arrays.copyOf(ch1, ch1.length+ch2.length);
  System.arraycopy(ch2, 0, ch3, ch1.length, ch2.length);
  System.out.println(ch3);//中國北京歡迎您
  /* String API提供了簡潔的連接運(yùn)算: */
  String str1="中國北京";
  String str2="歡迎您";
  String str3=str1.concat(str2);
  System.out.println(str3);//中國北京歡迎您
  /* 字符串轉(zhuǎn)大寫: */
  char[] ch4={'A','a','c','f'};
  char[] ch5=Arrays.copyOf(ch4, ch4.length);
  for(int i=0;i<ch5.length;i++){
   char c=ch5[i];
   if(c>='a' && c<='z'){
    ch5[i]=(char)(c+('A'-'a'));
   }
  }
  System.out.println(ch5);//AACF, 原數(shù)組ch4不變
  String str4="Aacf";
  String str5=str4.toUpperCase();//原字符串str4保持不變
  System.out.println(str5);//AACF
 }
}