Guava：google公司开发的一款Java类库扩展工具包_com.google.guava:guava

Guava是google公司开发的一款Java类库扩展工具包

文档

• https://github.com/google/guava
• https://github.com/google/guava/wiki
• https://guava.dev/releases/snapshot-jre/api/docs/
• https://mvnrepository.com/artifact/com.google.guava/guava

maven 依赖

<dependency>
  <groupId>com.google.guava</groupId>
  <artifactId>guava</artifactId>
  <version>31.1-jre</version>
</dependency>
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示例1：连接字符串

package com.example;


import com.google.common.base.Joiner;

import java.util.Arrays;

public class Demo {
    public static void main(String[] args) {

        // JDK 1.8
        String var1 = String.join("-", Arrays.asList("A", null, "C", "D"));
        System.out.println(var1);
        // A-null-C-D

        // guava
        Joiner joiner = Joiner.on("-").skipNulls();
        String var2 = joiner.join("A", null, "C", "D");
        System.out.println(var2);
        // A-C-D
    }
}

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示例2：统计元素出现次数

package com.example;


import com.google.common.collect.HashMultiset;
import com.google.common.collect.Multiset;

import java.util.Arrays;

public class Demo {
    public static void main(String[] args) {

        String[] words = {"A", "B", "C", "B"};

        // JDK 1.8
        Map<String, Integer> counts = new HashMap<String, Integer>();
        for (String word : words) {
            Integer count = counts.get(word);
            if (count == null) {
                counts.put(word, 1);
            } else {
                counts.put(word, count + 1);
            }
        }
        
        System.out.println(counts);
        // {A=1, B=2, C=1}

        // guava
        Multiset<String> multiset = HashMultiset.create();
        multiset.addAll(Arrays.asList(words));

        System.out.println(multiset);
        // [A, B x 2, C]
        System.out.println(multiset.count("B"));
        // 2
    }
}

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示例3：key对应集合

package com.example;


import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.Multimap;

public class Demo {
    public static void main(String[] args) {
        
        Multimap<String, Integer> multimap = ArrayListMultimap.create();
        multimap.put("A", 1);
        multimap.put("A", 2);
        multimap.put("B", 4);
        multimap.put("C", 5);

        System.out.println(multimap);
        // {A=[1, 2], B=[4], C=[5]}
    }
}

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示例4：list分组

5条数据，按照2个元素一组，进行分组

// JDK 1.8
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);

List<List<Integer>> partitionList = new ArrayList<>();


List<Integer> dataList = new ArrayList<>();
int size = 0;

for(Integer data : list) {
    size++;

    dataList.add(data);

    if(size >= 2) {
        partitionList.add(dataList);

        dataList = new ArrayList<>();
        size = 0;
    }
}

if (dataList.size() > 0){
    partitionList.add(dataList);
}

System.out.println(partitionList);
// [[1, 2], [3, 4], [5]]
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使用Lists.partition方法

// guava
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
List<List<Integer>> partition = Lists.partition(list, 2);
System.out.println(partition);
// [[1, 2], [3, 4], [5]]
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参考
Guava中这些Map的骚操作，让我的代码量减少了50%
一篇让你熟练掌握Google Guava包(全网最全)
Java中代码优化的30个小技巧