简单 Java 类型的 TreeMap
首先,我们创建一个空地图,并在其中插入一些元素:
Version >= Java SE 7
TreeMap<Integer, String> treeMap = new TreeMap<>();
Version < Java SE 7
TreeMap<Integer, String> treeMap = new TreeMap<Integer, String>();
treeMap.put(10, "ten");
treeMap.put(4, "four");
treeMap.put(1, "one");
treeSet.put(12, "twelve");
一旦我们在地图中有一些元素,我们就可以执行一些操作:
System.out.println(treeMap.firstEntry()); // Prints 1=one
System.out.println(treeMap.lastEntry()); // Prints 12=twelve
System.out.println(treeMap.size()); // Prints 4, since there are 4 elemens in the map
System.out.println(treeMap.get(12)); // Prints twelve
System.out.println(treeMap.get(15)); // Prints null, since the key is not found in the map
我们还可以使用 Iterator 或 foreach 循环迭代 map 元素。请注意,条目是根据其自然顺序打印的,而不是插入顺序:
Version >= Java SE 7
for (Entry<Integer, String> entry : treeMap.entrySet()) {
System.out.print(entry + " "); //prints 1=one 4=four 10=ten 12=twelve
}
Iterator<Entry<Integer, String>> iter = treeMap.entrySet().iterator();
while (iter.hasNext()) {
System.out.print(iter.next() + " "); //prints 1=one 4=four 10=ten 12=twelve
}