Java集合中的通用算法，开发效率翻倍

引言

Java在日常工作中用的非常多，每天日复一日的增删改查，集合作为最常见的数据结构为我们处理数据提供了很大的方便，集合中有一些常见的算法，比如：排序，二分查找，洗牌算法等等，本文主要介绍Java集合中常见的通用算法。

函数	作用
sort()	排序
shuffle()	进行洗牌
reverse()	颠倒元素的顺序
fill()	用指定值替换元素中的每个元素
copy()	创建从指定源到目标的元素副本
swap()	交换集合中两个元素的位置
addAll()	将一个集合的所有元素添加到其他集合中
binarySearch()	进行搜索
frequency()	返回元素在集合中出现的次数
disjoint()	检查两个元素是否包含某些共同元素
min() max()	分别用于查找最小和最大元素

Java集合中的通用算法

sort()排序

import java.util.ArrayList;
import java.util.Collections;public class Main {public static void main(String[] args) {// 初始化集合ArrayList<Integer> numbers = new ArrayList<>();// 添加元素numbers.add(4);numbers.add(2);numbers.add(3);System.out.println("Unsorted ArrayList: " + numbers);// 排序Collections.sort(numbers);System.out.println("Sorted ArrayList: " + numbers);}
}

输出

Unsorted ArrayList: [4, 2, 3]
Sorted ArrayList: [2, 3, 4]

shuffle()进行洗牌

import java.util.ArrayList;
import java.util.Collections;public class Main {public static void main(String[] args) {// 初始化集合ArrayList<Integer> numbers = new ArrayList<>();// 添加元素numbers.add(1);numbers.add(2);numbers.add(3);System.out.println("Sorted ArrayList: " + numbers);// 洗牌Collections.shuffle(numbers);System.out.println("ArrayList using shuffle: " + numbers);}
}

输出

Sorted ArrayList: [1, 2, 3]
ArrayList using shuffle: [1, 2, 3]

reverse()颠倒元素的顺序

import java.util.ArrayList;
import java.util.Collections;public class Main16 {public static void main(String[] args) {ArrayList<Integer> numbers = new ArrayList<>();numbers.add(1);numbers.add(2);System.out.println("ArrayList: " + numbers);Collections.reverse(numbers);System.out.println("Reversed ArrayList: " + numbers);}
}

输出

ArrayList: [1, 2]
Reversed ArrayList: [2, 1]

fill()用指定值替换集合中的每个元素

import java.util.ArrayList;
import java.util.Collections;public class Main16 {public static void main(String[] args) {ArrayList<Integer> numbers = new ArrayList<>();numbers.add(1);numbers.add(2);System.out.println("ArrayList: " + numbers);Collections.fill(numbers, 0);System.out.println("ArrayList using fill(): " + numbers);}
}

输出

ArrayList: [1, 2]
ArrayList using fill(): [0, 0]

copy()创建从指定源到目标的元素副本

import java.util.ArrayList;
import java.util.Collections;public class Main16 {public static void main(String[] args) {ArrayList<Integer> numbers1 = new ArrayList<>();numbers1.add(1);numbers1.add(2);System.out.println("ArrayList1: " + numbers1);ArrayList<Integer> numbers2 = new ArrayList<>();numbers2.add(3);numbers2.add(4);numbers2.add(5);numbers2.add(6);System.out.println("ArrayList2: " + numbers2);Collections.copy(numbers2, numbers1);System.out.println("ArrayList using copy(): " + numbers2);}
}

输出

ArrayList1: [1, 2]
ArrayList2: [3, 4, 5, 6]
ArrayList using copy(): [1, 2, 5, 6]

swap()交换集合中两个元素的位置

import java.util.ArrayList;
import java.util.Collections;public class Main16 {public static void main(String[] args) {ArrayList<Integer> numbers = new ArrayList<>();numbers.add(1);numbers.add(2);System.out.println("ArrayList: " + numbers);Collections.swap(numbers, 0,1);System.out.println("ArrayList using swap(): " + numbers);}
}

输出

ArrayList: [1, 2]
ArrayList using swap(): [2, 1]

addAll()将一个集合的所有元素添加到其他集合中

import java.util.ArrayList;public class Main16 {public static void main(String[] args) {ArrayList<Integer> numbers1 = new ArrayList<>();numbers1.add(1);numbers1.add(2);System.out.println("ArrayList1: " + numbers1);ArrayList<Integer> numbers2 = new ArrayList<>();numbers2.add(3);numbers2.add(4);System.out.println("ArrayList2: " + numbers2);numbers1.addAll(numbers2);System.out.println("ArrayList using addAll(): " + numbers1);}
}

输出

ArrayList1: [1, 2]
ArrayList2: [3, 4]
ArrayList using addAll(): [1, 2, 3, 4]

binarySearch()进行搜索

import java.util.ArrayList;
import java.util.Collections;public class Main16 {public static void main(String[] args) {ArrayList<Integer> numbers = new ArrayList<>();numbers.add(1);numbers.add(2);numbers.add(3);int pos = Collections.binarySearch(numbers, 3);System.out.println("The position of 3 is " + pos);}
}

输出

The position of 3 is 2

frequency()返回元素在集合中出现的次数

import java.util.ArrayList;
import java.util.Collections;public class Main16 {public static void main(String[] args) {ArrayList<Integer> numbers = new ArrayList<>();numbers.add(1);numbers.add(2);numbers.add(3);numbers.add(2);System.out.println("ArrayList: " + numbers);int count = Collections.frequency(numbers, 2);System.out.println("Count of 2: " + count);}
}

输出

ArrayList: [1, 2, 3, 2]
Count of 2: 2

disjoint()检查两个集合是否包含某些共同元素

import java.util.ArrayList;
import java.util.Collections;public class Main16 {public static void main(String[] args) {ArrayList<Integer> numbers = new ArrayList<>();numbers.add(1);numbers.add(2);numbers.add(3);numbers.add(2);System.out.println("ArrayList1: " + numbers);ArrayList<Integer> newNumbers = new ArrayList<>();newNumbers.add(5);newNumbers.add(6);System.out.println("ArrayList2: " + newNumbers);boolean value = Collections.disjoint(numbers, newNumbers);System.out.println("Two lists are disjoint: " + value);}
}

输出

ArrayList1: [1, 2, 3, 2]
ArrayList2: [2, 6]
Two lists are disjoint: false

min()方法max()分别用于查找最小和最大元素

import java.util.ArrayList;
import java.util.Collections;public class Main16 {public static void main(String[] args) {ArrayList<Integer> numbers = new ArrayList<>();numbers.add(1);numbers.add(2);numbers.add(3);int min = Collections.min(numbers);System.out.println("Minimum Element: " + min);int max = Collections.max(numbers);System.out.println("Maximum Element: " + max);}
}