46 lines
1.1 KiB
Markdown
46 lines
1.1 KiB
Markdown
- [[Map]]集合中的一种实现
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- 底层结构
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- JDK1.7前：[[数组]]+ [[链表]]
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- JDK1.7后：[[数组]]+[[链表]]+ [[红黑二叉树]]
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- 用法
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- ```java
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HashMap<String,String> datas = new HashMap<>();
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```
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- [[put]]
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- [[putAll]]
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- [[get]]
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- [[getOrDefault]]
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- 允许放[[null]]键null值
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- [[replace]]
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- [[remove]]
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- [[clear]]
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- [[keySet]]
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- [[values]]
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- [[去重]]
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- 依靠Hashcode和equals
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- HashSet的底层是HashMap的key
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- Keys要重写equals和hashCode
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- 遍历
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- [[forEach]]
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- ```java
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datas.forEach(new BiConsumer<Girl, Boy>() {
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@Override
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public void accept(Girl key, Boy value) {
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System.out.println("key=" + key + ",value" + value);
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}
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});
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```
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- 获得键的集合
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- ```java
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Set<Girl> keys = datas.keySet();
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for (Girl e : keys) {
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System.out.println("key=" + e + ",value=" + datas.get(e));
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}
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```
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- [[entrySet]]
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- ```java
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Set<Map.Entry<Girl, Boy>> entries = datas.entrySet();
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for (Map.Entry<Girl, Boy> e : entries {
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System.out.println("key=" + e.getKey() + ",value=" + e.getValue());
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}
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``` |