Guava tutorial collect some cases and write Google tool classes slowly

Reference resources

Article, understand guava
Translation of official documents

Achieve the goal

1. understand Lists Sets Maps And other common methods of collection classes
2. understand guava Collections2 and jdk Collections hutool CollectionUtil
3. understand guava ListenableFuture Of And Java Native Future Use

problem

1. How to get the iterator of the collection class
2. Collections Why are there so many internal classes ( To return a class object )

Collection classes

// map  Copy 
@Test
public void test4() throws IllegalAccessException {
    
    HashMap<String, String> hashMap = Maps.newHashMap();
    hashMap.put("1","A");
    hashMap.put("2","B");
    Map<String, String> res ;
    res = ImmutableMap.copyOf(hashMap);
    System.out.println(JSON.toJSONString(res));
}

Initialization of collection classes

//  Ordinary Collection The creation of 
List<String> list = Lists.newArrayList();
Set<String> set = Sets.newHashSet();
Map<String, String> map = Maps.newHashMap();
//  unchanged Collection The creation of 
ImmutableList<String> iList = ImmutableList.of("a", "b", "c");
ImmutableSet<String> iSet = ImmutableSet.of("e1", "e2");
ImmutableMap<String, String> iMap = ImmutableMap.of("k1", "v1", "k2", "v2");