在Java中所有的Map都实现了Map接口，因此所有的Map（如 HashMap, TreeMap, LinkedHashMap, Hashtable等）都可以用以下的方式去遍历。
方法1: 使用Lambda表达式
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| Map<String, String> map = new HashMap<>();
map.put("Java", "Java");
map.put("Python", "Python");
map.forEach((key, value) -> System.out.println("key = " + key + ", value = " + value));
map.forEach((key, value) -> {
System.out.println("key = " + key);
System.out.println("value = " + value);
});
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方法2: 在for循环中使用entrySet实现Map的遍历
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| Map<String, String> map = new HashMap<>();
map.put("Java", "Java");
map.put("Python", "Python");
for (Map.Entry<String, String> entry : map.entrySet()) {
String key = entry.getKey();
String value = entry.getValue();
System.out.println("key = " + key + ", value = " + value);
}
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方法3: 在for循环中遍历key或者values，一般适用于只需要Map中的key或者value时使用，在性能上比使用entrySet较好
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| Map<String, String> map = new HashMap<>();
map.put("Java", "Java");
map.put("Python", "Python");
for (String key : map.keySet()) {
System.out.println("key = " + key);
}
for (String value : map.values()) {
System.out.println("value = " + value);
}
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方法4: 通过Iterator遍历
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| Map<String, String> map = new HashMap<>();
map.put("Java", "Java");
map.put("Python", "Python");
Iterator<Map.Entry<String, String>> entries = map.entrySet().iterator();
while (entries.hasNext()) {
Map.Entry<String, String> entry = entries.next();
String key = entry.getKey();
String value = entry.getValue();
System.out.println("key = " + key + ", value = " + value);
}
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方法5: 通过键找值遍历，这种方式的效率比较低，因为本身从键取值是耗时的操作
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| Map<String, String> map = new HashMap<>();
map.put("Java", "Java");
map.put("Python", "Python");
for (String key : map.keySet()) {
String value = map.get(key);
System.out.println("key = " + key + ", value = " + value);
}
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