学习java第39天

1.StringBuffer可以追加字符

public class SyrinBufferDemo1 {
 public static void main(String[] args) {
  StringBuilder buf = new StringBuilder();
  System.out.println(buf.capacity());
  buf.append("张三").append("常说")
   .append("他爱打游戏");
  System.out.println(buf.capadity());
  System.out.println(buf);
 }
}

//16

//34

//张三常说他爱打游戏

2.StringBuffer的添加和删除功能

*Public StringBuffer append ( String str );

public StringBuffer insert  (  int offset , String str  );

*public StringBuffer deleteCharAt (  int  index );

public StringBuffer delete (   int   start  ,int  end );

public static void main(String[] args) {
StringBuffer sb =new StringBuffer();
sb.append("hehehe");
System.out.println("sb: "+ sb);
sb.insert(6, "hahahaha");
System.out.println(sb);
StringBuffer sb2= new StringBuffer();
sb2.append("hello").append("World");
System.out.println(sb2);
sb2.delete(5, 10); 
System.out.println(sb2);
sb2.deleteCharAt(4);
System.out.println(sb2);
}

3.stringBuffer性能比String性能高

public class StringInterview {
 public static void main(String[] args) {
  String result="";
  StringBuffer sbResult=new StringBuffer();
  int count=5000;
  long startTime=System.currentTimeMillis();
  for (int i = 0; i <count; i++)="" {<br="">   result=result+"a";
  }
  System.out.println("string时间差:"+(System.currentTimeMillis()-startTime));
   startTime=System.currentTimeMillis();
  for (int i = 0; i <count; i++)="" {<br="">   sbResult.append("a");
  }
  System.out.println("stringbuffer时间差:"+(System.currentTimeMillis()-startTime));
 }
}

//string时间差：32

//stringbuffer时间差：0

4.明天学习内容：StringBuilder类的使用