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50 lines
1.2 KiB
50 lines
1.2 KiB
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HashSet 和 TreeSet 源码解析
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---
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#### HashSet
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HashSet 就是维护一个不包含重复元素的集合。
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它的实现很简单，就是通过 HashMap 来做的。
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```java
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public class HashSet<E>
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extends AbstractSet<E>
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implements Set<E>, Cloneable, java.io.Serializable
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{
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private transient HashMap<E,Object> map;
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private static final Object PRESENT = new Object();
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public HashSet() {
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map = new HashMap<>();
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}
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public boolean add(E e) {
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return map.put(e, PRESENT)==null;
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}
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}
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```
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#### TreeSet
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TreeSet 大致的结构和 HashSet 相似，底层组合的是 TreeMap，所以继承了 TreeMap key 能够排序的功能，迭代的时候，也可以按照 key 的排序顺序进行迭代。
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```java
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public class TreeSet<E> extends AbstractSet<E>
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implements NavigableSet<E>, Cloneable, java.io.Serializable
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{
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private transient NavigableMap<E,Object> m;
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private static final Object PRESENT = new Object();
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public TreeSet() {
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this(new TreeMap<>());
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}
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public boolean add(E e) {
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return m.put(e, PRESENT)==null;
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}
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}
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```
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但是和 HashSet 不同的是，TreeSet 可以实现从头或从尾进行遍历，这时是 TreeSet 定义接口，让 TreeMap 去实现的。 |