在Java中，哪些集合类是线程安全的？

import java.util.*;
public class StackTest {
   public static void main (String[] args) {
      Stack<Integer> stack = new Stack<Integer>();
      stack.<strong>push</strong>(5);
      stack.<strong>push</strong>(7);
      stack.<strong>push</strong>(9);
      Integer num1 = (Integer)stack.<strong>pop</strong>();
      System.out.println("The element popped is: " + num1);
      Integer num2 = (Integer)stack.<strong>peek</strong>();
      System.out.println(" The element on stack top is: " + num2);
   }
}

The element popped is: 9
The element on stack top is: 7

import java.util.*;
public class VectorTest {
   public static void main(String[] arg) {
      Vector vector = new Vector();
      vector.<strong>add</strong>(9);
      vector.add(3);
      vector.add("ABC");
      vector.add(1);
      vector.add("DEF");
      System.out.println("The vector is: " + vector);
      vector.<strong>remove</strong>(1);
      System.out.println("The vector after an element is removed is: " + vector);
   }
}

The vector is: [9, 3, ABC, 1, DEF]
The vector after an element is removed is: [9, ABC, 1, DEF]