@ohos.util.TreeSet (Nonlinear Container TreeSet)

TreeSet is implemented based on TreeMap. In TreeSet, only value objects are processed. TreeSet can be used to store values, each of which must be unique.

HashSet stores data in a random order, whereas TreeSet stores data in sorted order. Both of them allow only unique elements. However, null values are allowed in HashSet, but not in TreeSet, because null values may affect the order of elements in the container.

Recommended use case: Use TreeSet when you need to store data in sorted order.

This topic uses the following to identify the use of generics:

• T: Type

NOTE

The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.

Modules to Import

import TreeSet from '@ohos.util.TreeSet';  

TreeSet

Attributes

System capability: SystemCapability.Utils.Lang

constructor

constructor(comparator?: (firstValue: T, secondValue: T) => boolean)

A constructor used to create a TreeSet instance. It supports sorting elements in ascending or descending order by using comparators.

System capability: SystemCapability.Utils.Lang

Parameters

Error codes

For details about the error codes, see Utils Error Codes.

Example

// Constructor.
let treeSet : TreeSet<string | number | boolean | Object> = new TreeSet();

// Use the comparator firstValue < secondValue if the elements are expected to be sorted in ascending order. Use firstValue > secondValue if the elements are expected to be sorted in descending order.
let treeSet : TreeSet<string> = new TreeSet<string>((firstValue: string, secondValue: string) : boolean => {return firstValue < secondValue});
treeSet.add("a");
treeSet.add("c");
treeSet.add("d");
treeSet.add("b");
let numbers = Array.from(treeSet.values())
for (let item of numbers) {
  console.log("TreeSet:" + item);
}

// When a custom type is inserted, a comparator must be provided.
class TestEntry{
  public id: number = 0;
}
let ts1: TreeSet<TestEntry> = new TreeSet<TestEntry>((t1: TestEntry, t2: TestEntry): boolean => {return t1.id > t2.id;});
let entry1: TestEntry = {
  id: 0
};
let entry2: TestEntry = {
  id: 1
}
ts1.add(entry1);
ts1.add(entry2);
console.log("treeSet: ", ts1.length);

isEmpty

isEmpty(): boolean

Checks whether this container is empty (contains no element).

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

const treeSet : TreeSet<string | number | boolean | Object>  = new TreeSet();
let result = treeSet.isEmpty();

has

has(value: T): boolean

Checks whether this container has the specified value.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let treeSet : TreeSet<number> = new TreeSet();
treeSet.add(123);
let result = treeSet.has(123);

getFirstValue

getFirstValue(): T

Obtains the value of the first element in this container.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let treeSet : TreeSet<string> = new TreeSet();
treeSet.add("squirrel");
treeSet.add("sparrow");
let result = treeSet.getFirstValue();

getLastValue

getLastValue(): T

Obtains the value of the last element in this container.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let treeSet : TreeSet<string> = new TreeSet();
treeSet.add("squirrel");
treeSet.add("sparrow");
let result = treeSet.getLastValue();

add

add(value: T): boolean

Adds an element to this container.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let treeSet : TreeSet<string> = new TreeSet();
let result = treeSet.add("squirrel");

remove

remove(value: T): boolean

Removes the element with the specified key from this container.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let treeSet : TreeSet<string> = new TreeSet();
treeSet.add("squirrel");
treeSet.add("sparrow");
let result = treeSet.remove("sparrow");

getLowerValue

getLowerValue(key: T): T

Obtains the value that is placed in front of the input key in this container.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let treeSet : TreeSet<string> = new TreeSet();
treeSet.add("squirrel");
treeSet.add("sparrow");
treeSet.add("gander");
let result = treeSet.getLowerValue("sparrow");

getHigherValue

getHigherValue(key: T): T

Obtains the value that is placed next to the input key in this container.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let treeSet : TreeSet<string> = new TreeSet();
treeSet.add("squirrel");
treeSet.add("sparrow");
treeSet.add("gander");
let result = treeSet.getHigherValue("sparrow");

popFirst

popFirst(): T

Removes the first element in this container.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let treeSet : TreeSet<string> = new TreeSet();
treeSet.add("squirrel");
treeSet.add("sparrow");
let result = treeSet.popFirst();

popLast

popLast(): T

Removes the last element in this container.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let treeSet : TreeSet<string> = new TreeSet();
treeSet.add("squirrel");
treeSet.add("sparrow");
let result = treeSet.popLast();

clear

clear(): void

Clears this container and sets its length to 0.

System capability: SystemCapability.Utils.Lang

Error codes

For details about the error codes, see Utils Error Codes.

Example

let treeSet : TreeSet<string> = new TreeSet();
treeSet.add("squirrel");
treeSet.add("sparrow");
treeSet.clear();

values

values(): IterableIterator<T>

Obtains an iterator that contains all the values in this container.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let treeSet : TreeSet<string> = new TreeSet();
treeSet.add("squirrel");
treeSet.add("sparrow");
let it = treeSet.values();
let t: IteratorResult<string> = it.next();
while(!t.done) {
  console.log("TreeSet: " + t.value);
  t = it.next()
}

forEach

forEach(callbackFn: (value?: T, key?: T, set?: TreeSet<T>) => void, thisArg?: Object): void

Uses a callback to traverse the elements in this container and obtain their position indexes.

System capability: SystemCapability.Utils.Lang

Parameters

callbackFn

Error codes

For details about the error codes, see Utils Error Codes.

Example

let treeSet : TreeSet<string> = new TreeSet();
treeSet.add("sparrow");
treeSet.add("gull");
treeSet.forEach((value ?: string, key ?: string) :void => {
  console.log("value:" + value, "key:" + key);
});

entries

entries(): IterableIterator<[T, T]>

Obtains an iterator that contains all the elements in this container.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let treeSet : TreeSet<string> = new TreeSet();
treeSet.add("squirrel");
treeSet.add("sparrow");
let it = treeSet.entries();
let t: IteratorResult<Object[]> = it.next();
while(!t.done) {
  console.log("TreeSet: " + t.value);
  t = it.next()
}

[Symbol.iterator]

[Symbol.iterator](): IterableIterator<T>

Obtains an iterator, each item of which is a JavaScript object.

NOTE

This API cannot be used in .ets files.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let treeSet : TreeSet<string> = new TreeSet();
treeSet.add("squirrel");
treeSet.add("sparrow");
let numbers = Array.from(treeSet.values())
// Method 1:
for (let item of numbers) {
  console.log("value:" + item);
}
// Method 2:
let iter = treeSet[Symbol.iterator]();
let temp: IteratorResult<string> = iter.next().value;
while(temp != undefined) {
  console.log("value:" + temp);
  temp = iter.next().value;
}