运行时出现“java.lang.NoClassDefFoundError”的解决方法

在用java命令运行.class文件时，总是出现exception in thread "main" java.lang.NoClassDefFoundError:

package scut.zeng.exam;

import java.io.Console;
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class MoveWord {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
while (true) {
System.out.printf("%nEnter your regex: ");
Pattern pattern = Pattern.compile(scanner.nextLine());
System.out.printf("Enter input string to search: ");
Matcher matcher = pattern.matcher(scanner.nextLine());
boolean found = false;
while (matcher.find()) {
System.out.printf(
"I found the text \"%s\" starting at index %d and ending at index %d.%n",
matcher.group(), matcher.start(), matcher.end()
);
found = true;
}
if (!found) {
System.out.printf("No match found.%n");
}
}
}
}

package scut.zeng.exam;