java String类常用方法练习小结

public class StringTest_1
{
 //对字符串数组进行排序
 public static void stringSort(String[] arr)
 {
 //采用冒泡排序
 for(int i=0;i<arr.length-1;i++)
 {
  for(int j=0;j<arr.length-1-i;j++)
  {
  //用compareTo方法进行字符串比较
  if(arr[j].compareTo(arr[j+1])>0)
  {
   String temp=arr[j];
   arr[j]=arr[j+1];
   arr[j+1]=temp;
  }
  }
 }
 showArray(arr);
 }
 //定义方法，以[str1,str2,str3]的格式来打印数组
 public static void showArray(String[] arr)
 {
 System.out.print("[");
 for(int i=0;i<arr.length;i++)
 {
  if(i!=arr.length-1)
  System.out.print(arr[i]+",");
  else
  {
  System.out.print(arr[i]+"]\n");
  }
 }
 }
 public static void main(String[] args) 
 {
 String arr[]={"nba","abc","cba","zz","qq","haha"};
 //打印数组
 showArray(arr);
 //对数组进行排序并输出
 stringSort(arr);
 }
}

public class StringTest_2 
{
 public static void main(String[] args) 
 {
 String str="abcqwabcedcxabcuabcjkabcnmbabc";
 //String str=null;
 try
 {
  int count=countChildStr(str,"abc");
  System.out.println("abc在"+str+"中出现的次数为："+count);
 }
 catch (NullPointerException ne)
 {
  System.out.println(ne);
 }
 catch(RuntimeException re)
 {
  System.out.println(re);
 }
 }
 public static int countChildStr(String str,String key)
 {
 if(str==null||key==null)
 {
  throw new NullPointerException("空指针异常,源字符串和子串都不能为NULL");
 }
 if(key=="")
 {throw new RuntimeException("调用不合法，子串要有内容");}
 int count=0,index=0;
 while((index=str.indexOf(key,index))!=-1)
 {
  count++;
  index+=key.length();
 }
 return count;
 }
}

public class StringTest_3
{
 public static void main(String[] args) 
 {
 //创建两个不为空的字符串
 String str1="abxczwsxcvdfas";
 //String str1=null;
 String str2="ghwsxcvxcdbgthnnnrfqwe";
 try
 {
  String str=searchMaxCommonStr(str1,str2);
  System.out.println("最大公共子串是："+str);
 }
 catch (NullPointerException ne)
 {
  System.out.println(ne);
 }
 }
 public static String searchMaxCommonStr(String str1,String str2)
 {
 if(str1==null||str2==null)
  throw new NullPointerException("空指针异常，参数不能为Null");
 //断定较长字符串和较短字符串
 String max=(str1.length()>str2.length())?str1:str2;
 String min=(str1.equals(max))?str2:str1;
 //按长度递减的方式取子串，从min.length~~1
 for(int i=min.length();i>0;i--)
 {
  for(int x=0,y=x+i;y<min.length();x++,y++)
  {
  String childStr=min.substring(x,y);
  //若较长字符串中包含此子串，则找到了
  //否则继续找
  if(max.contains(childStr))
   return childStr;
  }
 }
 return null;
 }
}

public class StringTest_4
{
 public static void main(String[] args) 
 {
 String str=" abc ws ";
 str=myTrim(str);
 System.out.println(str);
 }
 public static String myTrim(String s)
 {
 int begin=0,end=s.length()-1;
 //从头遍历
 while(begin<=end && s.charAt(begin)==' ')
 {
  begin++;
 }
 //从尾部遍历
 while(begin<=end && s.charAt(end)==' ')
 {
  end--;
 }
 return s.substring(begin,end+1);
 }
}