求List,Map,Set的交集，并集与差集

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应用场景

  在大数据的背景下，我们在做项目的时候往往使用单表在数据库中查询数据，然后多表在service层进行关联操作。比如说下面的情况就是如此，在这里我并不是展开讲多表之间如何实现解耦的单表查询操作，我只是针对其中的涉及多表关联的集合操作进行讲解。

ListMap集合操作

数据准备

List<String> list1 = Lists.newArrayList("a","b","c","f");
List<String> list2 = Lists.newArrayList("c","d","e","f");

交集

@Test
public void testIntersection(){
    list1.retainAll(list2);
    List<String> list3 = Lists.newArrayList("c","f");
    Assert.assertEquals(list3,list1);
    list1.forEach( str -> log.info("打印出的字符为：{}",str));
}

  执行结果：

[13:31:43.729] INFO  com.baishun.login.setOperation.ListOperation 24 lambda$testIntersection$0 - 打印出的字符为：c
[13:31:43.737] INFO  com.baishun.login.setOperation.ListOperation 24 lambda$testIntersection$0 - 打印出的字符为：f

并集

@Test
public void testUnion(){
    list1.addAll(list2);
    List<String> list3 = Lists.newArrayList("a","b","c","f","c","d","e","f");
    Assert.assertEquals(list3,list1);
    list1.forEach( str -> log.info("打印出的字符为：{}",str));
}

  执行结果：

[13:32:53.028] INFO  com.baishun.login.setOperation.ListOperation 35 lambda$testUnion$1 - 打印出的字符为：a
[13:32:53.035] INFO  com.baishun.login.setOperation.ListOperation 35 lambda$testUnion$1 - 打印出的字符为：b
[13:32:53.035] INFO  com.baishun.login.setOperation.ListOperation 35 lambda$testUnion$1 - 打印出的字符为：c
[13:32:53.036] INFO  com.baishun.login.setOperation.ListOperation 35 lambda$testUnion$1 - 打印出的字符为：f
[13:32:53.037] INFO  com.baishun.login.setOperation.ListOperation 35 lambda$testUnion$1 - 打印出的字符为：c
[13:32:53.037] INFO  com.baishun.login.setOperation.ListOperation 35 lambda$testUnion$1 - 打印出的字符为：d
[13:32:53.037] INFO  com.baishun.login.setOperation.ListOperation 35 lambda$testUnion$1 - 打印出的字符为：e
[13:32:53.037] INFO  com.baishun.login.setOperation.ListOperation 35 lambda$testUnion$1 - 打印出的字符为：f

差集

@Test
public void testSubtract(){
    list1.removeAll(list2);
    List<String> list3 = Lists.newArrayList();
    list3.add("a");
    list3.add("b");
    Assert.assertEquals(list3,list1);
    list1.forEach( str -> log.info("打印出的字符为：{}",str));
}

  执行结果：

[13:35:01.629] INFO  com.baishun.login.setOperation.ListOperation 48 lambda$testSubtract$2 - 打印出的字符为：a
[13:35:01.641] INFO  com.baishun.login.setOperation.ListOperation 48 lambda$testSubtract$2 - 打印出的字符为：b

Map集合操作

数据准备

ImmutableMap<String,String> immutableMap1 = ImmutableMap.of("a","a","b","b","c","c","f","f");
ImmutableMap<String,String> immutableMap2 = ImmutableMap.of("c","c","d","d","e","e","f","f");

MapDifference<String,String> difference = Maps.difference(immutableMap1,immutableMap2);

交集

@Test
public void testIntersection(){
    Map<String,String> commonMap = difference.entriesInCommon();
    Map<String,String> map3 = Maps.newHashMap();
    map3.put("c","c");
    map3.put("f","f");
    Assert.assertEquals(map3,commonMap);
    commonMap.forEach((k,v) -> {
        log.info("打印出的字符为：{}:{}",k,v);
    });
}

  执行结果：

[13:37:23.391] INFO  com.baishun.login.setOperation.MapOperation 33 lambda$testIntersection$0 - 打印出的字符为：c:c
[13:37:23.398] INFO  com.baishun.login.setOperation.MapOperation 33 lambda$testIntersection$0 - 打印出的字符为：f:f

并集

@Test
public void testUnion(){
    //将ImmutableMap转换成Map
    Map<String,String> map1 = Maps.newHashMap(immutableMap1);
    Map<String,String> map2 = Maps.newHashMap(immutableMap2);

    map1.putAll(map2);

    Map<String,String> map3 = Maps.newHashMap();
    map3.put("a","a");
    map3.put("b","b");
    map3.put("c","c");
    map3.put("d","d");
    map3.put("e","e");
    map3.put("f","f");
    Assert.assertEquals(map3,map1);
    map1.forEach((k,v) -> {
        log.info("打印出的字符为：{}:{}",k,v);
    });
}

  执行结果：

[13:38:06.784] INFO  com.baishun.login.setOperation.MapOperation 57 lambda$testUnion$1 - 打印出的字符为：a:a
[13:38:06.792] INFO  com.baishun.login.setOperation.MapOperation 57 lambda$testUnion$1 - 打印出的字符为：b:b
[13:38:06.793] INFO  com.baishun.login.setOperation.MapOperation 57 lambda$testUnion$1 - 打印出的字符为：c:c
[13:38:06.793] INFO  com.baishun.login.setOperation.MapOperation 57 lambda$testUnion$1 - 打印出的字符为：d:d
[13:38:06.793] INFO  com.baishun.login.setOperation.MapOperation 57 lambda$testUnion$1 - 打印出的字符为：e:e
[13:38:06.794] INFO  com.baishun.login.setOperation.MapOperation 57 lambda$testUnion$1 - 打印出的字符为：f:f

差集（左侧）

@Test
public void testLeftSubtract(){
    Map<String,String> leftMap = difference.entriesOnlyOnLeft();
    Map<String,String> map3 = Maps.newHashMap();
    map3.put("a","a");
    map3.put("b","b");
    Assert.assertEquals(map3,leftMap);
    leftMap.forEach((k,v) -> {
        log.info("打印出的字符为：{}:{}",k,v);
    });
}

  执行结果：

[13:39:22.543] INFO  com.baishun.login.setOperation.MapOperation 72 lambda$testLeftSubtract$2 - 打印出的字符为：a:a
[13:39:22.550] INFO  com.baishun.login.setOperation.MapOperation 72 lambda$testLeftSubtract$2 - 打印出的字符为：b:b

差集（右侧）

@Test
public void testRightSubtract(){
    Map<String,String> rightMap = difference.entriesOnlyOnRight();
    Map<String,String> map3 = Maps.newHashMap();
    map3.put("d","d");
    map3.put("e","e");
    Assert.assertEquals(map3,rightMap);
    rightMap.forEach((k,v) -> {
        log.info("打印出的字符为：{}:{}",k,v);
    });
}

  执行结果：

[13:40:07.171] INFO  com.baishun.login.setOperation.MapOperation 87 lambda$testRightSubtract$3 - 打印出的字符为：d:d
[13:40:07.180] INFO  com.baishun.login.setOperation.MapOperation 87 lambda$testRightSubtract$3 - 打印出的字符为：e:e

Set集合操作

数据准备

Set<String> set1 = Sets.newHashSet("a","b","c","f");
Set<String> set2 = Sets.newHashSet("c","d","e","f");

交集

@Test
public void testIntersection(){
    set1.retainAll(set2);
    Iterator<String> iterator = set1.iterator();
    Set<String> set3 = Sets.newHashSet("c","f");
    //断言
    Assert.assertEquals(set3,set1);
    while(iterator.hasNext()){
        log.info("打印出的字符为：{}",iterator.next());
    }
}

  执行结果：

[13:41:28.227] INFO  com.baishun.login.setOperation.SetOperation 28 testIntersection - 打印出的字符为：c
[13:41:28.233] INFO  com.baishun.login.setOperation.SetOperation 28 testIntersection - 打印出的字符为：f

并集

@Test
public void testUnion(){
    set1.addAll(set2);
    Iterator<String> iterator = set1.iterator();
    Set<String> set3 = Sets.newHashSet("a","b","c","f","d","e");
    //断言
    Assert.assertEquals(set3,set1);
    while(iterator.hasNext()){
        log.info("打印出的字符为：{}",iterator.next());
    }
}

  执行结果：

[13:42:10.658] INFO  com.baishun.login.setOperation.SetOperation 43 testUnion - 打印出的字符为：a
[13:42:10.666] INFO  com.baishun.login.setOperation.SetOperation 43 testUnion - 打印出的字符为：b
[13:42:10.667] INFO  com.baishun.login.setOperation.SetOperation 43 testUnion - 打印出的字符为：c
[13:42:10.669] INFO  com.baishun.login.setOperation.SetOperation 43 testUnion - 打印出的字符为：d
[13:42:10.670] INFO  com.baishun.login.setOperation.SetOperation 43 testUnion - 打印出的字符为：e
[13:42:10.670] INFO  com.baishun.login.setOperation.SetOperation 43 testUnion - 打印出的字符为：f

差集

@Test
public void testSubtract(){
    set1.removeAll(set2);
    Iterator<String> iterator = set1.iterator();
    Set<String> set3 = Sets.newHashSet("a","b");
    //断言
    Assert.assertEquals(set3,set1);
    while(iterator.hasNext()){
        log.info("打印出的字符为：{}",iterator.next());
    }
}

  执行结果：

[13:42:59.123] INFO  com.baishun.login.setOperation.SetOperation 58 testSubtract - 打印出的字符为：a
[13:42:59.130] INFO  com.baishun.login.setOperation.SetOperation 58 testSubtract - 打印出的字符为：b