- public static void main(String[] args) {<br> ListFor(2);<br> }<br><br> public static void ListFor(int a){<br> //测试list集合遍历(直接有四种遍历方式)<br> final ArrayList<Integer> integers = new ArrayList<>();<br> integers.add(1);<br> integers.add(2);<br> integers.add(3);<br> integers.add(4);<br> //测试set集合遍历(一般转换成数组进行遍历)<br> HashSet<String> strings = new HashSet<>();<br> strings.add("张三");<br> strings.add("123");<br> strings.add("张三");<br> //测试map集合遍历<br> HashMap<Integer, String> map = new HashMap<>();<br> map.put(1,"麻婆豆腐");<br> map.put(2,"红烧牛肉");<br> map.put(3,"狮子头");<br><br><br> //1.经典循坏遍历:效率最高遍历快，但是不适用于所有集合实用范围小<br> if (a==1) {<br> //list集合遍历<br> for (int i = 0; i < integers.size(); i++) {<br> System.out.println(integers.get(i));<br> }<br> //set集合遍历<br> Object[] objects = strings.toArray();<br> for (int i = 0; i < objects.length; i++) {<br> System.out.println(objects[i]);<br> }<br> }<br> //2.迭代器遍历:遍历时可以操作元素，但是相对于其他遍历方式效率比较慢<br> if (a==2){<br> //list集合遍历<br> Iterator<Integer> iterator = integers.iterator();<br> while (iterator.hasNext()){<br> System.out.print(iterator.next());<br> }<br> //set集合遍历<br> Iterator<String> iterator1 = strings.iterator();<br> while (iterator1.hasNext()){<br> System.out.println(iterator1.next());<br> }<br> //map集合遍历<br> Iterator<Map.Entry<Integer, String>> iterator2 = map.entrySet().iterator();<br> while (iterator2.hasNext()){<br> Map.Entry<Integer, String> entry = iterator2.next();<br> System.out.println(entry.getKey());<br> System.out.println(entry.getValue());<br> }<br> }<br> //3.加强for循环遍历:代码简洁，但是不能操作元素<br> if (a==3){<br> //list集合遍历<br> System.out.println("加强for循环遍历结果:");<br> for (Integer integer:integers){<br> System.out.println(integer);<br> }<br> //set集合遍历<br> for (String str:strings){<br> System.out.println(str);<br> }<br> //map集合遍历<br> for (Map.Entry<Integer, String> entry : map.entrySet()) {<br> System.out.println(entry.getKey());<br> System.out.println(entry.getValue());<br> }<br> }<br> //4.lambda表达式遍历<br> if (a==4){<br> System.out.println("lambda表达式遍历");<br>// JDK8之后才有的遍历<br>// integers.forEach(integer-> System.out.println(integer));<br> }<br> }
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