常用类demo--【J2SE】

StringBuffer类

public class TestStringBuffer{
public static void main(String[] args){
String s="Mircosoft";
char[] a={'a' ,'b' ,'c'};
StringBuffer sb1=new StringBuffer(s);
sb1.append('/').append("IBM").append('/').append("Sun");
System.out.println(sb1);
StringBuffer sb2=new StringBuffer("数字");
for (int i=0;i<=9;i++){
sb2.append(i);
}
System.out.println(sb2);
sb2.delete(8,sb2.length());
System.out.println(sb2);
System.out.println(sb2.reverse());
}

}

File类

import java.io.*;
//把所有的孩子的递归都列出来
public class FileList{
public static void main(String[] args){
File f=new File("d:/A");
tree(f);
}
private static void tree(File f){
File[] childs=f.listFiles();
for(int i =0;i<childs.length;i++){
System.out.println(childs[i].getName());
if(childs[i].isDirectory()){
tree(childs[i]);
}
}
}
}

枚举类型：

public class TestEnum{

public enum MyColor{red,green,blue};

public static void main(String[] args){
MyColor m=MyColor.red;
switch(m){
case red:
System.out.println("red");
break;
case green:
System.out.println("green");
break;
default:
System.out.println("default");
}

System.out.println(m);
}
}