I will also summarize the Map method as a review. It will be updated as needed.
put(K key, V value) Associates the specified value with the specified key on this map.
Map<String,String> map = new HashMap<String,String>() {
{ put("apple", "Apple");
put("orange", "Orange");
put("banana", "banana");
}
};
System.out.println(map);
//The key and value are set at the same time as the map is initialized,
//It is OK to execute separately as follows.
//map.put("apple", "Apple");
//map.put("orange", "Orange");
//map.put("banana", "banana");
{orange=Orange, banana=banana, apple=Apple}
get(Object key) Returns the value to which the specified key is mapped. Returns null if this map does not contain a mapping for that key.
Map<String,String> map = new HashMap<String,String>() {
{ put("apple", "Apple");
put("orange", "Orange");
put("banana", "banana");
}
};
System.out.println(map.get("apple"));
System.out.println(map.get("app"));
Apple
null
size() Returns the number of key-value mappings in this map.
Map<String,String> map = new HashMap<String,String>() {
{ put("apple", "Apple");
put("orange", "Orange");
put("banana", "banana");
}
};
System.out.println(map.size());
3
containsKey(Object key) Returns true if the specified key mapping is included in this map.
Map<String,String> map = new HashMap<String,String>() {
{ put("apple", "Apple");
put("orange", "Orange");
put("banana", "banana");
}
};
System.out.println(map.containsKey("orange"));
System.out.println(map.containsKey("banana"));
System.out.println(map.containsKey("oge"));
true
true
false
containsValue(Object value) Returns true if the map maps one or more keys to the specified value.
Map<String,String> map = new HashMap<String,String>() {
{ put("apple", "Apple");
put("orange", "Orange");
put("banana", "banana");
}
};
System.out.println(map.containsValue("Apple"));
System.out.println(map.containsValue("Orange"));
System.out.println(map.containsValue("range"));
true
true
false
clear() Remove all mappings from the map.
Map<String,String> map = new HashMap<String,String>() {
{ put("apple", "Apple");
put("orange", "Orange");
put("banana", "banana");
}
};
map.clear()
System.out.println(map);
{}
entrySet() Returns a Set view of the mappings contained in this map.
Map<String,String> map = new HashMap<String,String>() {
{ put("apple", "Apple");
put("orange", "Orange");
put("banana", "banana");
}
};
System.out.println(map.entrySet());
[orange=Orange, banana=banana, apple=Apple]
keySet() Returns a Set view of the keys contained in this map.
Map<String,String> map = new HashMap<String,String>() {
{ put("apple", "Apple");
put("orange", "Orange");
put("banana", "banana");
}
};
//You can get the key at once
System.out.println(map.keySet());
//To get the keys one by one, use the extended for statement as shown below.
for(String s : map.keySet()) {
System.out.println(s);
}
[orange, banana, apple]
orange
banana
apple
values() Returns a Collection view of the values contained in this map.
Map<String,String> map = new HashMap<String,String>() {
{ put("apple", "Apple");
put("orange", "Orange");
put("banana", "banana");
}
};
//You can get the value at once
System.out.println(map.values());
//If you want to get the values one by one, use the extended for statement as shown below.
for(String s : map.values()) {
System.out.println(s);
}
[Orange,banana,Apple]
Orange
banana
Apple
remove(Object key) Remove the key mapping (if any) from this map.
Map<String,String> map = new HashMap<String,String>() {
{ put("apple", "Apple");
put("orange", "Orange");
put("banana", "banana");
}
};
map.remove("orange");
System.out.println(map);
//orange has been removed
{banana=banana, apple=Apple}
remove(Object key, Object value) Deletes the entry for the specified key only if the specified key is currently mapped to the specified value.
Map<String,String> map = new HashMap<String,String>() {
{ put("apple", "Apple");
put("orange", "Orange");
put("banana", "banana");
}
};
//If you set a value that does not exist, it will not be deleted and will remain as it is
map.remove("orange","Olesi");
System.out.println(map);
//If you set a key that does not exist, it will not be deleted and will remain as it is
map.remove("oge","Orange");
System.out.println(map);
//If you set an existing key and value, it will be deleted
map.remove("orange","Orange");
System.out.println(map);
{orange=Orange, banana=banana, apple=Apple}
{orange=Orange, banana=banana, apple=Apple}
{banana=banana, apple=Apple}
replace(K key, V value) Replaces the entry for that key only if the specified key is currently mapped to some value.
Map<String,String> map = new HashMap<String,String>() {
{ put("apple", "Apple");
put("orange", "Orange");
put("banana", "banana");
}
};
//If you set a key that does not exist, the Map remains as it is
map.replace("bana", "Banana Nanana");
System.out.println(map);
//If you set an existing key, the value associated with it will be replaced.
map.replace("banana", "Banana Nanana");
System.out.println(map);
{orange=Orange, banana=banana, apple=Apple}
{orange=Orange, banana=Banana Nanana, apple=Apple}
replace(K key, V oldValue, V newValue) Replaces the entry for the specified key only if it is currently mapped to the specified value.
Map<String,String> map = new HashMap<String,String>() {
{ put("apple", "Apple");
put("orange", "Orange");
put("banana", "banana");
}
};
//If you specify an old value that does not exist, it will not be replaced
map.replace("bana", "Bana","Natto");
System.out.println(map);
//Specifying an existing key and value replaces the value
map.replace("banana", "banana","Natto");
System.out.println(map);
{orange=Orange, banana=banana, apple=Apple}
{orange=Orange, banana=Natto, apple=Apple}
isEmpty() Returns true if this map does not retain a key-value mapping.
Map<String,String> map = new HashMap<String,String>();
System.out.println(map.isEmpty());
true
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