String  str = "hello你好嗎,我很好 thank you";  
String reg = "[\u2E80-\u9FFF]";  
Pattern pat = Pattern.compile(reg);    
Matcher mat = pat.matcher(str);   
String repickStr = mat.replaceAll("");  
System.out.println("過濾中文後: "+repickStr);

Demo：

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class T {

	
	/**
	 * 過濾字母
	 * @param alphabet
	 * @return
	 */
	public static String filterAlphabet(String alphabet){
		return alphabet.replaceAll("[A-Za-z]", "");
	}
	
	/**
	 * 過濾數字
	 * @param digital
	 * @return
	 */
	public static String filterDigital(String digital){
		return digital.replaceAll("[0-9]", "");
	}
	
	/**
	 * 過濾漢字
	 * @param chin
	 * @return
	 */
	public static String filterChinese(String chin){
		return chin.replaceAll("[\\u4e00-\\u9fa5]", "");
	}
	
	/**
	 * 過濾 字母、數字、漢字
	 * @param character
	 * @return
	 */
	public static String filterAll(String character){
		return character.replaceAll("[a-zA-Z0-9\\u4e00-\\u9fa5]", "");
    }
	
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		String  str = "hello你好嗎,我很好 thank you";  
        String reg = "[\u2E80-\u9FFF]";  
        Pattern pat = Pattern.compile(reg);    
        Matcher mat = pat.matcher(str);   
        String repickStr = mat.replaceAll("");  
        System.out.println("過濾中文後: "+repickStr);  
		
        System.out.println("-----------------");
        
		System.out.println(filterAlphabet("123abc你好"));
		System.out.println(filterDigital("123abc你好"));
		System.out.println(filterChinese("123abc你好"));
		System.out.println(filterAll("123abc你好"));
	}

}