public static void main(String[] args) throws IOException {
    String str="284_300_16_331_34_363_379_395";
    String temp;
    if("_".equals(str.substring(str.length()-1,str.length()))){
        temp=str.substring(0,str.lastIndexOf("_"));
    }else{
        temp=str;
    }
    System.out.println(temp.substring(temp.lastIndexOf("_")+1,temp.length()));
}

------解决方案--------------------
探讨


Java code

String s = "284_300_16_331_34_363_379_395_";
String[] ss= s.split("_");
System.out.println(ss[ss.length - 1]);


------解决方案--------------------
String s = "284_300_16_331_34_363_379_39_";
		String[] ss= s.split("_");
		System.out.println(ss[ss.length - 1]);

------解决方案--------------------
呃。。。lz说这个字符串长度不固定，也就是说如果很长的话用“_”分割会产生一个长度很长的数组。这样会不会太占用资源。如果这样实现的话 大家看有没有什么问题:
Pattern pattern = Pattern.compile("[0-9]*$");
Matcher matcher = pattern.matcher("234_1231_234_34_34_345_45_34");\
if(matcher.find())
   System.out.println(matcher.group());

------解决方案--------------------
探讨


Java code

String s = "284_300_16_331_34_363_379_395_";
String[] ss= s.split("_");
System.out.println(ss[ss.length - 1]);


------解决方案--------------------
Java code

        String s ="284_300_16_331_34_363_379_395_";
    String s1=s;
    if(s.lastIndexOf("_")==s.length()-1){
        s1 =s.substring(0,s.length()-1);
    }
    String last =s1.substring(s1.lastIndexOf("_")+1);
    System.out.println(last);

------解决方案--------------------
Java code

  String _s = "284_300_16_331_34_363_379_395_";
  String _s0 = _s.substring(0, _s.length-1);
  int _last_index = _s0.lastIndexOf("_");
  String _result = _s0.substring(_last_index+1);

------解决方案--------------------
Pattern pattern = Pattern.compile("[0-9]{2,3}$");
Matcher matcher = pattern.matcher("234_1231_234_34_34_345_45_34");
if(matcher.find())
 System.out.println(matcher.group());

------解决方案--------------------
String str="284_300_16_331_34_363_379_395_";
		String[] s=str.split("_");
		System.out.println(s[s.length-1]);

------解决方案--------------------
Java code


//这是楼上各位的，都很强大
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Split5 {
    public static void main(String args[]) {

        String s2 = "284_300_16_331_34_363_379_395_";
        String[] ss = s2.split("_");
        System.out.println(ss[ss.length - 1]);

        //
        String str = "284_300_16_331_34_363_379_395";
        String temp;
        if ("_".equals(str.substring(str.length() - 1, str.length()))) {
            temp = str.substring(0, str.lastIndexOf("_"));
        } else {
            temp = str;
        }
        System.out.println(temp.substring(temp.lastIndexOf("_") + 1, temp
                .length()));
        
        //
        String s ="284_300_16_331_34_363_379_395_";
        String s1=s;
        if(s.lastIndexOf("_")==s.length()-1){
            s1 =s.substring(0,s.length()-1);
        }
        String last =s1.substring(s1.lastIndexOf("_")+1);
        System.out.println(last);

        
        //
        String sq = "284_300_16_331_34_363_379_395_";
        String _s0 = sq.substring(0, sq.length()-1);
        int _last_index = _s0.lastIndexOf("_");
        String _result = _s0.substring(_last_index+1);
        System.out.println(_result);


        //
        Pattern pattern = Pattern.compile("[0-9]{2,3}$");
        Matcher matcher = pattern.matcher("234_1231_234_34_34_345_45_34");
        if(matcher.find())
          System.out.println(matcher.group());

    }

}