java String 方法的使用

import java.util.Random;

public class SetString {

/**
* @param args
*/
public static void main(String[] args) {
// TODO 自动生成方法存根
String str = "abcd123" ;

int size = 5 ;

System.out.println(isNullStr(str));
System.out.println(isNumber(str));
System.out.println(firstUpper(str));
System.out.println(getRandomnum(size));
System.out.println(repStr(str,"jiangyang"));
}

//判断str是否为空
public static boolean isNullStr(String str)
{
return (str == null || str.equals("null") || "".equals(str))?true:false ;
}

//是否为数字
public static boolean isNumber(String str)
{
try{
Double.valueOf(str) ;
return true ;
}catch(Exception e){
return false ;
}
}

//首字符大写
public static String firstUpper(String str)
{
return isNullStr(str)?str:str.substring(0, 1).toUpperCase()+str.substring(1) ;
}

//产生随机数
public static String getRandomnum(int size)
{
char[] c = ("0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ") .toCharArray();
Random rr = new Random() ;
StringBuffer sb = new StringBuffer() ;
for(int i=0 ; i<size ; i++)
{
sb.append(c[Math.abs(rr.nextInt(1000))%c.length]) ;
}
return sb.toString() ;
}

//替换字符
public static String repStr(String str,String str1)
{
if(isNullStr(str)||isNullStr(str1)) return null ;
//return str.substring(0,2)+str.replace(str.substring(2,3), str1)+str.substring(3) ;
return str.replace(str.substring(2,3), str1);
}
}

//截取
String str1 = "abcd,";
String str2 = "e";
str1.replace(str1.substring(4,5), str2);
System.out.println(str1.substring(0,str1.length()-1));

//拼凑字符
String[] str = {"1","2","3","4"};
for(int i=0;i<str.length;i++){
if(i==0){
sbf.append(str[i]);
}else{
sbf.append(",").append(str[i]);
}
}

System.out.println(sbf.toString());
if(sbf.toString().equals("")){
System.out.println("1");
}

运行结果 ：

false
false
Abcd123
L6jps
abjiangyangd123