利用java 怎么将Map转化为二维数组

import java.util.HashMap; import java.util.Iterator; import java.util.Map;  public class Test {   public static void main(String[] args) {     int a = 0, b = 0, c = 0;     // 第一种:通过Map.keySet()遍历Map及将Map转化为二维数组     Map<String, String> map1 = new HashMap<String, String>();     map1.put("012013012013", "张三");     map1.put("012013012014", "张四");     String[][] group1 = new String[map1.size()][2];     System.out.println("第一种:通过Map.keySet()遍历map1的key和value");     for (String key : map1.keySet()) {        System.out.println("key = " + key + " and value = " + map1.get(key));        group1[a][0] = key;       group1[a][1] = map1.get(key);       a++;     }      System.out.println("map1.size()为：" + map1.size() + ",a为：" + a + "，group1数组的长度为：" + group1.length);     System.out.println("----------------------------------------------------");     for(int n = 0; n < group1.length; n++) {       System.out.println("key = " + group1[n][0] + " and value = " + group1[n][1]);      }          // 第二种:通过Map.entrySet()使用iterator()遍历Map及将Map转化为二维数组     Map<String, String> map2 = new HashMap<String, String>();     map2.put("112013012013", "李三");     map2.put("112013012014", "李四");     System.out.println("\n" + "第二种:通过Map.entrySet()使用iterator()遍历map2的key和value");     Iterator<Map.Entry<String, String>> iterator = map2.entrySet().iterator();      String[][] group2 = new String[map2.size()][2];     while (iterator.hasNext()) {        Map.Entry<String, String> entry = iterator.next();               System.out.println("key = " + entry.getKey() + " and value = " + entry.getValue());       group2[b][0] = entry.getKey();       group2[b][1] = entry.getValue();       b++;     }      System.out.println("map2.size()为：" + map2.size() + ",b为：" + b + "，group2数组的长度为：" + group2.length);     System.out.println("----------------------------------------------------");     for(int n = 0; n < group2.length; n++) {       System.out.println("key = " + group2[n][0] + " and value = " + group2[n][1]);      }          // 第三种:通过Map.entrySet()遍历遍历Map及将Map转化为二维数组     Map<String, String> map = new HashMap<String, String>();     map.putAll(map1);     map.putAll(map2);       String[][] group3 = new String[map.size()][2];     System.out.println("\n" + "第三种:通过Map.entrySet()遍历map的key和value ");        for (Map.Entry<String, String> entry : map.entrySet()) {        System.out.println("key = " + entry.getKey() + " and value = " + entry.getValue());        group3[c][0] = entry.getKey();       group3[c][1] = entry.getValue();       c++;     }     System.out.println("map.size()为：" + map.size() + ",c为：" + c + "，group3数组的长度为：" + group3.length);     System.out.println("----------------------------------------------------");     for(int n = 0; n < group3.length; n++) {       System.out.println("key = " + group3[n][0] + " and value = " + group3[n][1]);      }        } }