1 Collection集合
1.1 常用集合的体系
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Map集合的主要体系
HashMap集合 实现类
TreeMap集合 实现类
LinkedHashMap集合 实现类
HashTable集合 实现类
ConccurentHashMap集合 实现类
提示: 有关Map中的方法可不止上面这些，其他方法可以自行查看API学习。 注意:这张图只是我们常用的集合有这些，不是说就只有这些集合。
1.2 Map 常用API
目标：Map集合的常用API(重点中的重点) key=value
public V put(K key, V value): 把指定的键与指定的值添加到Map集合中。public V remove(Object key): 把指定的键 所对应的键值对元素 在Map集合中删除，返回被删除元素的值。public V get(Object key) 根据指定的键，在Map集合中获取对应的值。public Set<K> keySet(): 获取Map集合中所有的键，存储到Set集合中。public Set<Map.Entry<K,V>> entrySet(): 获取到Map集合中所有的键值对对象的集合(Set集合)。public boolean containKey(Object key):判断该集合中是否有此键。public boolean containValue(Object value):判断该集合中是否有此值。
public static void main(String
[] args
) {
Map
<String , Integer> maps
= new HashMap<>();
maps
.put("iphoneX",10);
maps
.put("娃娃",30);
maps
.put("iphoneX",100);
maps
.put("huawei",1000);
maps
.put("生活用品",10);
maps
.put("手表",10);
System
.out
.println(maps
);
System
.out
.println(maps
.isEmpty());
Integer value
= maps
.get("娃娃");
System
.out
.println(value
);
System
.out
.println(maps
.remove("iphoneX"));
System
.out
.println(maps
);
System
.out
.println(maps
.containsKey("iphoneX"));
System
.out
.println(maps
.containsKey("生活用品"));
System
.out
.println(maps
.containsValue(10));
System
.out
.println(maps
.containsValue(30));
System
.out
.println(maps
.containsValue(10000));
Set
<String> keys
= maps
.keySet();
System
.out
.println(keys
);
Collection
<Integer> values
= maps
.values();
System
.out
.println(values
);
System
.out
.println(maps
.size());
Map
<String,Integer> maps2
= new HashMap<>();
maps2
.put("xiaoMi" , 1);
maps2
.put("🔨手机" , 10);
maps2
.put("手表" , 10000);
maps
.putAll(maps2
);
System
.out
.println(maps
);
}
2 HashMap 遍历方式
Map集合的遍历方式是全部集合都可以直接使用的,Map集合的遍历方式有：3种。 1）“键找值”的方式遍历：先获取Map集合全部的键，再根据遍历键找值。 2）“键值对”的方式遍历：难度较大。 3）JDK 1.8开始之后的新技术：Lambda表达式。（暂时了解）
2.1 for循环键找值
遍历方式：先提取Map集合全部键的Set集合，再遍历键的Set集合，然后通过键找值。
public static void main(String
[] args
) {
Map
<String , Integer> maps
= new HashMap<>();
maps
.put("娃娃", 30);
maps
.put("iphoneX", 100);
maps
.put("huawei", 1000);
maps
.put("生活用品", 10);
maps
.put("手表", 10);
System
.out
.println(maps
);
Set
<String> keys
= maps
.keySet();
for (String key
: keys
) {
System
.out
.println(key
+ " = " + maps
.get(key
));
}
}
2.2 foreach遍历
public static void main(String
[] args
) {
Map
<String , Integer> maps
= new HashMap<>();
maps
.put("娃娃",30);
maps
.put("iphoneX",100);
maps
.put("huawei",1000);
maps
.put("生活用品",10);
maps
.put("手表",10);
System
.out
.println(maps
);
Set
<Map
.Entry
<String, Integer>> entries
= maps
.entrySet();
for (Map
.Entry
<String, Integer> entry
: entries
) {
String key
= entry
.getKey();
Integer value
= entry
.getValue();
System
.out
.println(key
+ "===>" + value
);
}
}
2.3 forEach 的Lambda表达式
JDK 1.8开始之后的新技术Lambda表达式。
public static void main(String
[] args
) {
Map
<String, Integer> maps
= new HashMap<>();
maps
.put("娃娃", 30);
maps
.put("iphoneX", 100);
maps
.put("huawei", 1000);
maps
.put("生活用品", 10);
maps
.put("手表", 10);
System
.out
.println(maps
);
maps
.forEach((k
, v
) -> {
System
.out
.println(k
+ "==>" + v
);
});
}
2.4 map 自定义引用数据类型
public class Orange {
private String name
;
private double weight
;
private String price
;
......
}
public static void main(String
[] args
) {
Map
<String, Orange> maps
= new HashMap<>();
Orange o1
= new Orange("黄橘子", 20.2, "贼便宜");
Orange o2
= new Orange("黑橘子", 230.2, "贼便宜");
Orange o3
= new Orange("绿橘子", 20.2, "便宜");
Orange o4
= new Orange("臭橘子", 220.2, "贼便宜");
maps
.put("广州 ", o1
);
maps
.put("梅州 ", o2
);
maps
.put("上海 ", o3
);
maps
.put("深圳 ", o4
);
System
.out
.println(maps
);
}
3 LinkedHashMap
LinkedHashMap是HashMap的子类。 – 添加的元素按照键有序，不重复的。 HashSet集合相当于是HashMap集合的键都不带值。 LinkedHashSet集合相当于是LinkedHashMap集合的键都不带值。 底层原理完全一样，都是基于哈希表按照键存储数据的， 只是HashMap或者LinkedHashMap的键都多一个附属值。
public static void main(String
[] args
) {
Map
<String, Integer> maps
= new LinkedHashMap<>();
maps
.put("inhone", 10);
maps
.put("娃娃", 100);
maps
.put("huawei", 1000);
maps
.put("生活用品", 10);
maps
.put("手表", 19);
System
.out
.println(maps
);
}
4 TreeHashMap
TreeMap集合按照键是可排序不重复的键值对集合。(默认升序) TreeMap集合按照键排序的特点与TreeSet是完全一样的。 小结： TreeMap集合和TreeSet集合都是排序不重复集合 TreeSet集合的底层是基于TreeMap，只是键没有附属值而已。 所以TreeMap集合指定大小规则有2种方式：
直接为对象的类实现比较器规则接口Comparable，重写比较方法（拓展方式）直接为集合设置比较器Comparator对象,重写比较方法.优先使用集合自带比较器比较!
public class Pig implements Comparable{
private String name
;
private double price
;
private double weight
;
.......
@Override
public boolean equals(Object o
) {
if (this == o
) return true;
if (o
== null
|| getClass() != o
.getClass()) return false;
Pig pig
= (Pig
) o
;
return Double
.compare(pig
.price
, price
) == 0 &&
Double
.compare(pig
.weight
, weight
) == 0 &&
Objects
.equals(name
, pig
.name
);
}
@Override
public int hashCode() {
return Objects
.hash(name
, price
, weight
);
}
@Override
public int compareTo(Object o
) {
Pig p
= (Pig
) o
;
return Double
.compare(this.weight
, p
.weight
);
}
}
public static void main(String
[] args
) {
Map
<Integer, String> maps
= new TreeMap<>();
maps
.put(1000000, "张三");
maps
.put(1000000, "张三1");
maps
.put(10000, "李四");
maps
.put(10, "王五");
maps
.put(24244, "张麻子");
System
.out
.println(maps
);
Map
<String,Pig> pigs
= new TreeMap<>();
pigs
.put("荷兰", new Pig("🐖佩奇", 99.5, 500.0));
pigs
.put("澳大利亚", new Pig("🐖乔治", 99.4, 605.0));
pigs
.put("山上", new Pig("🐗野猪", 199.4, 305.0));
pigs
.put("山上2", new Pig("🐗野猪", 199.4, 305.0));
System
.out
.println(pigs
);
Map
<Pig, String> pigs2
= new TreeMap<>(new Comparator<Pig>() {
@Override
public int compare(Pig o1
, Pig o2
) {
return Double
.compare(o1
.getPrice(), o2
.getPrice()) != 0 ? Double
.compare(o1
.getPrice(), o2
.getPrice()) : 1;
}
});
pigs2
.put(new Pig("🐖佩奇", 99.5, 500.0), "荷兰1");
pigs2
.put(new Pig("🐖乔治", 99.4, 605.0), "澳大利亚2");
pigs2
.put(new Pig("🐗野猪", 199.4, 305.0), "山上3");
pigs2
.put(new Pig("🐗野猪", 199.4, 305.0), "山上4");
System
.out
.println(pigs2
);
}
5 HashTable
线程安全性能低
5 ConccurentHashMap
线程安全性能高
