Java : TreeMap with Examples
February 17, 2024 
June 30, 2022
TreeMap (Java SE 18 & JDK 18) API Examples.
You will find code examples on most TreeMap methods.
Summary
A Red-Black tree based NavigableMap implementation. The map is sorted according to the natural ordering of its keys, or by a Comparator provided at map creation time, depending on which constructor is used.
final var map = new TreeMap<String, Integer>();
System.out.println(map); // {}
map.put("a", 10);
map.put("b", 20);
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
System.out.println(map.get("a")); // 10
System.out.println(map.get("b")); // 20
System.out.println(map.get("X")); // null
map.remove("b");
System.out.println(map); // {a=10, c=30}
final var treeMap = new TreeMap<String, Integer>();
treeMap.put("ccc", 10);
treeMap.put("ddd", 20);
treeMap.put("aaa", 30);
treeMap.put("bbb", 40);
System.out.println(treeMap); // {aaa=30, bbb=40, ccc=10, ddd=20}
final var hashMap = new HashMap<String, Integer>();
hashMap.put("ccc", 10);
hashMap.put("ddd", 20);
hashMap.put("aaa", 30);
hashMap.put("bbb", 40);
System.out.println(hashMap); // {aaa=30, ccc=10, bbb=40, ddd=20}
Constructors
TreeMap ()
Constructs a new, empty tree map, using the natural ordering of its keys.
final var map = new TreeMap<String, Integer>();
System.out.println(map); // {}
System.out.println(map.isEmpty()); // true
map.put("b", 10);
map.put("a", 20);
map.put("c", 30);
System.out.println(map); // {a=20, b=10, c=30}
System.out.println(map.size()); // 3
final var map = new TreeMap<Integer, String>();
map.put(100, "a");
map.put(999, "b");
map.put(-200, "c");
System.out.println(map); // {-200=c, 100=a, 999=b}
TreeMap (Comparator<? super K> comparator)
Constructs a new, empty tree map, ordered according to the given comparator.
final var src = Map.of("bbb", 10, "aaa", 20, "ccc", 30);
final var map1 = new TreeMap<String, Integer>();
map1.putAll(src);
System.out.println(map1); // {aaa=20, bbb=10, ccc=30}
final var map2 = new TreeMap<String, Integer>(Comparator.reverseOrder());
map2.putAll(src);
System.out.println(map2); // {ccc=30, bbb=10, aaa=20}
TreeMap (Map<? extends K,? extends V> m)
Constructs a new tree map containing the same mappings as the given map, ordered according to the natural ordering of its keys.
final var m = Map.of("b", 10, "a", 20, "c", 30);
final var map = new TreeMap<>(m);
System.out.println(map); // {a=20, b=10, c=30}
System.out.println(map.size()); // 3
TreeMap (SortedMap<K,? extends V> m)
Constructs a new tree map containing the same mappings and using the same ordering as the specified sorted map.
final var m = new TreeMap<String, Integer>(Comparator.reverseOrder());
m.put("a", 10);
m.put("b", 20);
m.put("c", 30);
System.out.println(m); // {c=30, b=20, a=10}
final var map = new TreeMap<>(m);
System.out.println(map); // {c=30, b=20, a=10}
System.out.println(map.size()); // 3
Methods
Map.Entry<K,V> ceilingEntry (K key)
Returns a key-value mapping associated with the least key greater than or equal to the given key, or null if there is no such key.
final var map = new TreeMap<String, Integer>();
map.put("b", 10);
map.put("d", 20);
map.put("f", 30);
System.out.println(map); // {b=10, d=20, f=30}
System.out.println(map.ceilingEntry("a")); // b=10
System.out.println(map.ceilingEntry("b")); // b=10
System.out.println(map.ceilingEntry("c")); // d=20
System.out.println(map.ceilingEntry("d")); // d=20
System.out.println(map.ceilingEntry("e")); // f=30
System.out.println(map.ceilingEntry("f")); // f=30
System.out.println(map.ceilingEntry("g")); // null
K ceilingKey (K key)
Returns the least key greater than or equal to the given key, or null if there is no such key.
final var map = new TreeMap<String, Integer>();
map.put("b", 10);
map.put("d", 20);
map.put("f", 30);
System.out.println(map); // {b=10, d=20, f=30}
System.out.println(map.ceilingKey("a")); // b
System.out.println(map.ceilingKey("b")); // b
System.out.println(map.ceilingKey("c")); // d
System.out.println(map.ceilingKey("d")); // d
System.out.println(map.ceilingKey("e")); // f
System.out.println(map.ceilingKey("f")); // f
System.out.println(map.ceilingKey("g")); // null
void clear ()
Removes all of the mappings from this map.
final var map = new TreeMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
System.out.println(map); // {a=1, b=2, c=3}
System.out.println(map.size()); // 3
map.clear();
System.out.println(map); // {}
System.out.println(map.size()); // 0
Object clone ()
Returns a shallow copy of this TreeMap instance.
final var map = new TreeMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
System.out.println(map); // {a=1, b=2, c=3}
final var cloned = map.clone();
System.out.println(cloned); // {a=1, b=2, c=3}
System.out.println(cloned.getClass()); // class java.util.TreeMap
Comparator<? super K> comparator ()
Returns the comparator used to order the keys in this map, or null if this map uses the natural ordering of its keys.
final var map = new TreeMap<String, Integer>();
System.out.println(map); // {}
final var comparator = map.comparator();
System.out.println(comparator); // null
final var map = new TreeMap<String, Integer>(Comparator.reverseOrder());
System.out.println(map); // {}
final var comparator = map.comparator();
System.out.println(comparator.equals(Comparator.reverseOrder())); // true
final var map = new TreeMap<String, Integer>(String.CASE_INSENSITIVE_ORDER);
System.out.println(map); // {}
final var comparator = map.comparator();
System.out.println(comparator.equals(String.CASE_INSENSITIVE_ORDER)); // true
V compute (K key, BiFunction<? super K,? super V,? extends V> remappingFunction)
Attempts to compute a mapping for the specified key and its current mapped value (or null if there is no current mapping).
final var map = new TreeMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
System.out.println(map); // {a=1, b=2, c=3}
final var func = new BiFunction<String, Integer, Integer>() {
@Override
public Integer apply(String key, Integer value) {
if (value == null) {
return -100;
} else {
return value * 10;
}
}
};
final var ret1 = map.compute("a", func);
System.out.println(ret1); // 10
System.out.println(map); // {a=10, b=2, c=3}
final var ret2 = map.compute("b", func);
System.out.println(ret2); // 20
System.out.println(map); // {a=10, b=20, c=3}
final var ret3 = map.compute("c", func);
System.out.println(ret3); // 30
System.out.println(map); // {a=10, b=20, c=30}
final var ret4 = map.compute("x", func);
System.out.println(ret4); // -100
System.out.println(map); // {a=10, b=20, c=30, x=-100}
final var map = new TreeMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
System.out.println(map); // {a=1, b=2, c=3}
final var ret = map.compute("b", (key, value) -> null);
System.out.println(ret); // null
System.out.println(map); // {a=1, c=3}
V computeIfAbsent (K key, Function<? super K,? extends V> mappingFunction)
If the specified key is not already associated with a value (or is mapped to null), attempts to compute its value using the given mapping function and enters it into this map unless null.
final var map = new TreeMap<String, String>();
map.put("a", "aaa");
map.put("b", "bbb");
System.out.println(map); // {a=aaa, b=bbb}
final var func = new Function<String, String>() {
@Override
public String apply(String key) {
if ("c".equals(key)) {
return "ccc";
} else {
return null;
}
}
};
final var ret1 = map.computeIfAbsent("a", func);
System.out.println(ret1); // aaa
System.out.println(map); // {a=aaa, b=bbb}
final var ret2 = map.computeIfAbsent("b", func);
System.out.println(ret2); // bbb
System.out.println(map); // {a=aaa, b=bbb}
final var ret3 = map.computeIfAbsent("c", func);
System.out.println(ret3); // ccc
System.out.println(map); // {a=aaa, b=bbb, c=ccc}
final var ret4 = map.computeIfAbsent("d", func);
System.out.println(ret4); // null
System.out.println(map); // {a=aaa, b=bbb, c=ccc}
final var map = new TreeMap<String, List<String>>();
System.out.println(map); // {}
map.computeIfAbsent("a", (key) -> new ArrayList<>()).add("a-1");
System.out.println(map); // {a=[a-1]}
map.computeIfAbsent("a", (key) -> new ArrayList<>()).add("a-2");
System.out.println(map); // {a=[a-1, a-2]}
map.computeIfAbsent("b", (key) -> new ArrayList<>()).add("b-1");
System.out.println(map); // {a=[a-1, a-2], b=[b-1]}
V computeIfPresent (K key, BiFunction<? super K,? super V,? extends V> remappingFunction)
If the value for the specified key is present and non-null, attempts to compute a new mapping given the key and its current mapped value.
final var map = new TreeMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
System.out.println(map); // {a=1, b=2, c=3}
final var func = new BiFunction<String, Integer, Integer>() {
@Override
public Integer apply(String key, Integer value) {
return value * 10;
}
};
final var ret1 = map.computeIfPresent("a", func);
System.out.println(ret1); // 10
System.out.println(map); // {a=10, b=2, c=3}
final var ret2 = map.computeIfPresent("b", func);
System.out.println(ret2); // 20
System.out.println(map); // {a=10, b=20, c=3}
final var ret3 = map.computeIfPresent("c", func);
System.out.println(ret3); // 30
System.out.println(map); // {a=10, b=20, c=30}
final var ret4 = map.computeIfPresent("X", func);
System.out.println(ret4); // null
System.out.println(map); // {a=10, b=20, c=30}
final var map = new TreeMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
System.out.println(map); // {a=1, b=2, c=3}
final var ret = map.computeIfPresent("b", (k, v) -> null);
System.out.println(ret); // null
System.out.println(map); // {a=1, c=3}
boolean containsKey (Object key)
Returns true if this map contains a mapping for the specified key.
final var map = new TreeMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
System.out.println(map); // {a=1, b=2, c=3}
System.out.println(map.containsKey("a")); // true
System.out.println(map.containsKey("b")); // true
System.out.println(map.containsKey("c")); // true
System.out.println(map.containsKey("X")); // false
System.out.println(map.containsKey("")); // false
boolean containsValue (Object value)
Returns true if this map maps one or more keys to the specified value.
final var map = new TreeMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
map.put("x", 3);
System.out.println(map); // {a=1, b=2, c=3, x=3}
System.out.println(map.containsValue(0)); // false
System.out.println(map.containsValue(1)); // true
System.out.println(map.containsValue(2)); // true
System.out.println(map.containsValue(3)); // true
System.out.println(map.containsValue(4)); // false
NavigableSet<K> descendingKeySet ()
Returns a reverse order NavigableSet view of the keys contained in this map.
final var map = new TreeMap<String, Integer>();
map.put("a", 10);
map.put("b", 20);
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
final var descKeys = map.descendingKeySet();
System.out.println(descKeys); // [c, b, a]
map.put("d", 40);
System.out.println(map); // {a=10, b=20, c=30, d=40}
System.out.println(descKeys); // [d, c, b, a]
descKeys.remove("b");
System.out.println(map); // {a=10, c=30, d=40}
System.out.println(descKeys); // [d, c, a]
NavigableMap<K,V> descendingMap ()
Returns a reverse order view of the mappings contained in this map.
final var map = new TreeMap<String, Integer>();
map.put("a", 10);
map.put("b", 20);
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
final var descMap = map.descendingMap();
System.out.println(descMap); // {c=30, b=20, a=10}
map.put("d", 40);
System.out.println(map); // {a=10, b=20, c=30, d=40}
System.out.println(descMap); // {d=40, c=30, b=20, a=10}
descMap.remove("b");
System.out.println(map); // {a=10, c=30, d=40}
System.out.println(descMap); // {d=40, c=30, a=10}
Set<Map.Entry<K,V>> entrySet ()
Returns a Set view of the mappings contained in this map.
final var map = new TreeMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
System.out.println(map); // {a=1, b=2, c=3}
final var entries = map.entrySet();
System.out.println(entries); // [a=1, b=2, c=3]
map.replace("b", 20);
System.out.println(map); // {a=1, b=20, c=3}
System.out.println(entries); // [a=1, b=20, c=3]
entries.remove(Map.entry("a", 1));
System.out.println(map); // {b=20, c=3}
System.out.println(entries); // [b=20, c=3]
for (final var entry : entries) {
entry.setValue(entry.getValue() * 10);
}
System.out.println(map); // {b=200, c=30}
System.out.println(entries); // [b=200, c=30]
Map.Entry<K,V> firstEntry ()
Returns a key-value mapping associated with the least key in this map, or null if the map is empty.
final var map = new TreeMap<String, Integer>();
System.out.println(map); // {}
System.out.println(map.firstEntry()); // null
map.put("b", 20);
System.out.println(map); // {b=20}
System.out.println(map.firstEntry()); // b=20
map.put("c", 30);
System.out.println(map); // {b=20, c=30}
System.out.println(map.firstEntry()); // b=20
map.put("a", 10);
System.out.println(map); // {a=10, b=20, c=30}
System.out.println(map.firstEntry()); // a=10
K firstKey ()
Returns the first (lowest) key currently in this map.
final var map = new TreeMap<String, Integer>();
System.out.println(map); // {}
map.put("b", 20);
System.out.println(map); // {b=20}
System.out.println(map.firstKey()); // b
map.put("c", 30);
System.out.println(map); // {b=20, c=30}
System.out.println(map.firstKey()); // b
map.put("a", 10);
System.out.println(map); // {a=10, b=20, c=30}
System.out.println(map.firstKey()); // a
final var map = new TreeMap<String, Integer>();
System.out.println(map); // {}
try {
map.firstKey();
} catch (NoSuchElementException e) {
System.out.println(e);
}
// Result
// ↓
//java.util.NoSuchElementException
Map.Entry<K,V> floorEntry (K key)
Returns a key-value mapping associated with the greatest key less than or equal to the given key, or null if there is no such key.
final var map = new TreeMap<String, Integer>();
map.put("b", 10);
map.put("d", 20);
map.put("f", 30);
System.out.println(map); // {b=10, d=20, f=30}
System.out.println(map.floorEntry("a")); // null
System.out.println(map.floorEntry("b")); // b=10
System.out.println(map.floorEntry("c")); // b=10
System.out.println(map.floorEntry("d")); // d=20
System.out.println(map.floorEntry("e")); // d=20
System.out.println(map.floorEntry("f")); // f=30
System.out.println(map.floorEntry("g")); // f=30
K floorKey (K key)
Returns the greatest key less than or equal to the given key, or null if there is no such key.
final var map = new TreeMap<String, Integer>();
map.put("b", 10);
map.put("d", 20);
map.put("f", 30);
System.out.println(map); // {b=10, d=20, f=30}
System.out.println(map.floorKey("a")); // null
System.out.println(map.floorKey("b")); // b
System.out.println(map.floorKey("c")); // b
System.out.println(map.floorKey("d")); // d
System.out.println(map.floorKey("e")); // d
System.out.println(map.floorKey("f")); // f
System.out.println(map.floorKey("g")); // f
V get (Object key)
Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
final var map = new TreeMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
System.out.println(map); // {a=1, b=2, c=3}
System.out.println(map.get("a")); // 1
System.out.println(map.get("b")); // 2
System.out.println(map.get("c")); // 3
System.out.println(map.get("X")); // null
System.out.println(map.get("")); // null
SortedMap<K,V> headMap (K toKey)
Returns a view of the portion of this map whose keys are strictly less than toKey.
final var map = new TreeMap<String, Integer>();
map.put("x", 10);
map.put("y", 20);
map.put("z", 30);
System.out.println(map); // {x=10, y=20, z=30}
final var headMap = map.headMap("z");
System.out.println(headMap); // {x=10, y=20}
map.put("a", 40);
System.out.println(map); // {a=40, x=10, y=20, z=30}
System.out.println(headMap); // {a=40, x=10, y=20}
headMap.remove("x");
System.out.println(map); // {a=40, y=20, z=30}
System.out.println(headMap); // {a=40, y=20}
final var map = new TreeMap<String, Integer>();
map.put("a", 10);
map.put("b", 20);
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
System.out.println(map.headMap("a")); // {}
System.out.println(map.headMap("b")); // {a=10}
System.out.println(map.headMap("c")); // {a=10, b=20}
System.out.println(map.headMap("d")); // {a=10, b=20, c=30}
NavigableMap<K,V> headMap (K toKey, boolean inclusive)
Returns a view of the portion of this map whose keys are less than (or equal to, if inclusive is true) toKey.
final var map = new TreeMap<String, Integer>();
map.put("x", 10);
map.put("y", 20);
map.put("z", 30);
System.out.println(map); // {x=10, y=20, z=30}
final var headMap = map.headMap("y", true);
System.out.println(headMap); // {x=10, y=20}
map.put("a", 40);
System.out.println(map); // {a=40, x=10, y=20, z=30}
System.out.println(headMap); // {a=40, x=10, y=20}
headMap.remove("x");
System.out.println(map); // {a=40, y=20, z=30}
System.out.println(headMap); // {a=40, y=20}
final var map = new TreeMap<String, Integer>();
map.put("a", 10);
map.put("b", 20);
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
System.out.println(map.headMap("a")); // {}
System.out.println(map.headMap("a", true)); // {a=10}
System.out.println(map.headMap("b")); // {a=10}
System.out.println(map.headMap("b", true)); // {a=10, b=20}
System.out.println(map.headMap("c")); // {a=10, b=20}
System.out.println(map.headMap("c", true)); // {a=10, b=20, c=30}
System.out.println(map.headMap("d")); // {a=10, b=20, c=30}
System.out.println(map.headMap("d", true)); // {a=10, b=20, c=30}
Map.Entry<K,V> higherEntry (K key)
Returns a key-value mapping associated with the least key strictly greater than the given key, or null if there is no such key.
final var map = new TreeMap<String, Integer>();
map.put("b", 10);
map.put("d", 20);
map.put("f", 30);
System.out.println(map); // {b=10, d=20, f=30}
System.out.println(map.higherEntry("a")); // b=10
System.out.println(map.higherEntry("b")); // d=20
System.out.println(map.higherEntry("c")); // d=20
System.out.println(map.higherEntry("d")); // f=30
System.out.println(map.higherEntry("e")); // f=30
System.out.println(map.higherEntry("f")); // null
System.out.println(map.higherEntry("g")); // null
K higherKey (K key)
Returns the least key strictly greater than the given key, or null if there is no such key.
final var map = new TreeMap<String, Integer>();
map.put("b", 10);
map.put("d", 20);
map.put("f", 30);
System.out.println(map); // {b=10, d=20, f=30}
System.out.println(map.higherKey("a")); // b
System.out.println(map.higherKey("b")); // d
System.out.println(map.higherKey("c")); // d
System.out.println(map.higherKey("d")); // f
System.out.println(map.higherKey("e")); // f
System.out.println(map.higherKey("f")); // null
System.out.println(map.higherKey("g")); // null
Set<K> keySet ()
Returns a Set view of the keys contained in this map.
final var map = new TreeMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
System.out.println(map); // {a=1, b=2, c=3}
final var keys = map.keySet();
System.out.println(keys); // [a, b, c]
map.put("d", 4);
System.out.println(map); // {a=1, b=2, c=3, d=4}
System.out.println(keys); // [a, b, c, d]
keys.remove("a");
System.out.println(map); // {b=2, c=3, d=4}
System.out.println(keys); // [b, c, d]
Map.Entry<K,V> lastEntry ()
Returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.
final var map = new TreeMap<String, Integer>();
System.out.println(map); // {}
System.out.println(map.lastEntry()); // null
map.put("b", 20);
System.out.println(map); // {b=20}
System.out.println(map.lastEntry()); // b=20
map.put("a", 10);
System.out.println(map); // {a=10, b=20}
System.out.println(map.lastEntry()); // b=20
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
System.out.println(map.lastEntry()); // c=30
K lastKey ()
Returns the last (highest) key currently in this map.
final var map = new TreeMap<String, Integer>();
System.out.println(map); // {}
map.put("b", 20);
System.out.println(map); // {b=20}
System.out.println(map.lastKey()); // b
map.put("a", 10);
System.out.println(map); // {a=10, b=20}
System.out.println(map.lastKey()); // b
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
System.out.println(map.lastKey()); // c
final var map = new TreeMap<String, Integer>();
System.out.println(map); // {}
try {
map.lastKey();
} catch (NoSuchElementException e) {
System.out.println(e);
}
// Result
// ↓
//java.util.NoSuchElementException
Map.Entry<K,V> lowerEntry (K key)
Returns a key-value mapping associated with the greatest key strictly less than the given key, or null if there is no such key.
final var map = new TreeMap<String, Integer>();
map.put("b", 10);
map.put("d", 20);
map.put("f", 30);
System.out.println(map); // {b=10, d=20, f=30}
System.out.println(map.lowerEntry("a")); // null
System.out.println(map.lowerEntry("b")); // null
System.out.println(map.lowerEntry("c")); // b=10
System.out.println(map.lowerEntry("d")); // b=10
System.out.println(map.lowerEntry("e")); // d=20
System.out.println(map.lowerEntry("f")); // d=20
System.out.println(map.lowerEntry("g")); // f=30
K lowerKey (K key)
Returns the greatest key strictly less than the given key, or null if there is no such key.
final var map = new TreeMap<String, Integer>();
map.put("b", 10);
map.put("d", 20);
map.put("f", 30);
System.out.println(map); // {b=10, d=20, f=30}
System.out.println(map.lowerKey("a")); // null
System.out.println(map.lowerKey("b")); // null
System.out.println(map.lowerKey("c")); // b
System.out.println(map.lowerKey("d")); // b
System.out.println(map.lowerKey("e")); // d
System.out.println(map.lowerKey("f")); // d
System.out.println(map.lowerKey("g")); // f
V merge (K key, V value, BiFunction<? super V,? super V,? extends V> remappingFunction)
If the specified key is not already associated with a value or is associated with null, associates it with the given non-null value.
final var map = new TreeMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
System.out.println(map); // {a=1, b=2, c=3}
final var func = new BiFunction<Integer, Integer, Integer>() {
@Override
public Integer apply(Integer oldValue, Integer newValue) {
return oldValue + newValue;
}
};
final var ret1 = map.merge("a", 1000, func);
System.out.println(ret1); // 1001
System.out.println(map); // {a=1001, b=2, c=3}
final var ret2 = map.merge("b", 1000, func);
System.out.println(ret2); // 1002
System.out.println(map); // {a=1001, b=1002, c=3}
final var ret3 = map.merge("c", 1000, func);
System.out.println(ret3); // 1003
System.out.println(map); // {a=1001, b=1002, c=1003}
final var ret4 = map.merge("d", 1000, func);
System.out.println(ret4); // 1000
System.out.println(map); // {a=1001, b=1002, c=1003, d=1000}
final var ret5 = map.merge("b", 1000, (k, v) -> null);
System.out.println(ret5); // null
System.out.println(map); // {a=1001, c=1003, d=1000}
Map.Entry<K,V> pollFirstEntry ()
Removes and returns a key-value mapping associated with the least key in this map, or null if the map is empty.
final var map = new TreeMap<String, Integer>();
map.put("a", 10);
map.put("b", 20);
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
System.out.println(map.pollFirstEntry()); // a=10
System.out.println(map); // {b=20, c=30}
System.out.println(map.pollFirstEntry()); // b=20
System.out.println(map); // {c=30}
System.out.println(map.pollFirstEntry()); // c=30
System.out.println(map); // {}
System.out.println(map.pollFirstEntry()); // null
Map.Entry<K,V> pollLastEntry ()
Removes and returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.
final var map = new TreeMap<String, Integer>();
map.put("a", 10);
map.put("b", 20);
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
System.out.println(map.pollLastEntry()); // c=30
System.out.println(map); // {a=10, b=20}
System.out.println(map.pollLastEntry()); // b=20
System.out.println(map); // {a=10}
System.out.println(map.pollLastEntry()); // a=10
System.out.println(map); // {}
System.out.println(map.pollLastEntry()); // null
V put (K key, V value)
Associates the specified value with the specified key in this map.
final var map = new TreeMap<String, Integer>();
System.out.println(map); // {}
System.out.println(map.put("a", 1)); // null
System.out.println(map); // {a=1}
System.out.println(map.put("b", 2)); // null
System.out.println(map); // {a=1, b=2}
System.out.println(map.put("c", 3)); // null
System.out.println(map); // {a=1, b=2, c=3}
System.out.println(map.put("a", 999)); // 1
System.out.println(map); // {a=999, b=2, c=3}
void putAll (Map<? extends K,? extends V> map)
Copies all of the mappings from the specified map to this map.
final var map = new TreeMap<String, Integer>();
System.out.println(map); // {}
map.putAll(Map.of());
System.out.println(map); // {}
map.putAll(Map.of("a", 1, "b", 2));
System.out.println(map); // {a=1, b=2}
map.putAll(Map.of("c", 3, "d", 4, "e", 5));
System.out.println(map); // {a=1, b=2, c=3, d=4, e=5}
map.putAll(Map.of("a", 901, "b", 902, "z", 100));
System.out.println(map); // {a=901, b=902, c=3, d=4, e=5, z=100}
V remove (Object key)
Removes the mapping for this key from this TreeMap if present.
final var map = new TreeMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
System.out.println(map); // {a=1, b=2, c=3}
System.out.println(map.remove("b")); // 2
System.out.println(map); // {a=1, c=3}
System.out.println(map.remove("z")); // null
System.out.println(map); // {a=1, c=3}
int size ()
Returns the number of key-value mappings in this map.
final var map = new TreeMap<String, Integer>();
System.out.println(map); // {}
System.out.println(map.size()); // 0
map.put("a", 1);
System.out.println(map); // {a=1}
System.out.println(map.size()); // 1
map.put("b", 2);
System.out.println(map); // {a=1, b=2}
System.out.println(map.size()); // 2
map.put("c", 3);
System.out.println(map); // {a=1, b=2, c=3}
System.out.println(map.size()); // 3
NavigableMap<K,V> subMap (K fromKey, boolean fromInclusive, K toKey, boolean toInclusive)
Returns a view of the portion of this map whose keys range from fromKey to toKey.
final var map = new TreeMap<String, Integer>();
map.put("x", 10);
map.put("y", 20);
map.put("z", 30);
System.out.println(map); // {x=10, y=20, z=30}
final var subMap = map.subMap("a", true, "y", true);
System.out.println(subMap); // {x=10, y=20}
map.put("a", 40);
System.out.println(map); // {a=40, x=10, y=20, z=30}
System.out.println(subMap); // {a=40, x=10, y=20}
subMap.remove("x");
System.out.println(map); // {a=40, y=20, z=30}
System.out.println(subMap); // {a=40, y=20}
final var map = new TreeMap<String, Integer>();
map.put("a", 10);
map.put("b", 20);
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
System.out.println(map.subMap("a", true, "c", true)); // {a=10, b=20, c=30}
System.out.println(map.subMap("a", true, "c", false)); // {a=10, b=20}
System.out.println(map.subMap("a", false, "c", true)); // {b=20, c=30}
System.out.println(map.subMap("a", false, "c", false)); // {b=20}
System.out.println(map.subMap("a", true, "a", false)); // {}
System.out.println(map.subMap("a", true, "b", false)); // {a=10}
System.out.println(map.subMap("a", true, "c", false)); // {a=10, b=20}
System.out.println(map.subMap("a", true, "d", false)); // {a=10, b=20, c=30}
System.out.println(map.subMap("a", true, "d", false)); // {a=10, b=20, c=30}
System.out.println(map.subMap("b", true, "d", false)); // {b=20, c=30}
System.out.println(map.subMap("c", true, "d", false)); // {c=30}
System.out.println(map.subMap("d", true, "d", false)); // {}
SortedMap<K,V> subMap (K fromKey, K toKey)
Returns a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive.
final var map = new TreeMap<String, Integer>();
map.put("x", 10);
map.put("y", 20);
map.put("z", 30);
System.out.println(map); // {x=10, y=20, z=30}
final var subMap = map.subMap("a", "z");
System.out.println(subMap); // {x=10, y=20}
map.put("a", 40);
System.out.println(map); // {a=40, x=10, y=20, z=30}
System.out.println(subMap); // {a=40, x=10, y=20}
subMap.remove("x");
System.out.println(map); // {a=40, y=20, z=30}
System.out.println(subMap); // {a=40, y=20}
final var map = new TreeMap<String, Integer>();
map.put("a", 10);
map.put("b", 20);
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
System.out.println(map.subMap("a", "a")); // {}
System.out.println(map.subMap("a", "b")); // {a=10}
System.out.println(map.subMap("a", "c")); // {a=10, b=20}
System.out.println(map.subMap("a", "d")); // {a=10, b=20, c=30}
System.out.println(map.subMap("a", "d")); // {a=10, b=20, c=30}
System.out.println(map.subMap("b", "d")); // {b=20, c=30}
System.out.println(map.subMap("c", "d")); // {c=30}
System.out.println(map.subMap("d", "d")); // {}
SortedMap<K,V> tailMap (K fromKey)
Returns a view of the portion of this map whose keys are greater than or equal to fromKey.
final var map = new TreeMap<String, Integer>();
map.put("a", 10);
map.put("b", 20);
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
final var tailMap = map.tailMap("b");
System.out.println(tailMap); // {b=20, c=30}
map.put("d", 40);
System.out.println(map); // {a=10, b=20, c=30, d=40}
System.out.println(tailMap); // {b=20, c=30, d=40}
tailMap.remove("b");
System.out.println(map); // {a=10, c=30, d=40}
System.out.println(tailMap); // {c=30, d=40}
final var map = new TreeMap<String, Integer>();
map.put("a", 10);
map.put("b", 20);
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
System.out.println(map.tailMap("a")); // {a=10, b=20, c=30}
System.out.println(map.tailMap("b")); // {b=20, c=30}
System.out.println(map.tailMap("c")); // {c=30}
System.out.println(map.tailMap("d")); // {}
NavigableMap<K,V> tailMap (K fromKey, boolean inclusive)
Returns a view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) fromKey.
final var map = new TreeMap<String, Integer>();
map.put("a", 10);
map.put("b", 20);
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
final var tailMap = map.tailMap("a", false);
System.out.println(tailMap); // {b=20, c=30}
map.put("d", 40);
System.out.println(map); // {a=10, b=20, c=30, d=40}
System.out.println(tailMap); // {b=20, c=30, d=40}
tailMap.remove("b");
System.out.println(map); // {a=10, c=30, d=40}
System.out.println(tailMap); // {c=30, d=40}
final var map = new TreeMap<String, Integer>();
map.put("a", 10);
map.put("b", 20);
map.put("c", 30);
System.out.println(map); // {a=10, b=20, c=30}
System.out.println(map.tailMap("a")); // {a=10, b=20, c=30}
System.out.println(map.tailMap("a", false)); // {b=20, c=30}
System.out.println(map.tailMap("b")); // {b=20, c=30}
System.out.println(map.tailMap("b", false)); // {c=30}
System.out.println(map.tailMap("c")); // {c=30}
System.out.println(map.tailMap("c", false)); // {}
Collection<V> values ()
Returns a Collection view of the values contained in this map.
final var map = new TreeMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
System.out.println(map); // {a=1, b=2, c=3}
final var values = map.values();
System.out.println(values); // [1, 2, 3]
map.replace("b", 20);
System.out.println(map); // {a=1, b=20, c=3}
System.out.println(values); // [1, 20, 3]
values.remove(1);
System.out.println(map); // {b=20, c=3}
System.out.println(values); // [20, 3]
//values.add(4); // UnsupportedOperationException
Methods declared in AbstractMap
Methods declared in Map
equals, forEach, getOrDefault, hashCode, isEmpty, putIfAbsent, remove, replace, replace, replaceAll
Please see the link below.
Related posts
- API Examples