Guava is a set of core Java libraries from Google that includes new collection types (such as multimap and multiset), immutable collections, a graph library, and utilities for concurrency, I/O, hashing, caching, primitives, strings, and more! It is widely used on most Java projects within Google, and widely used by many other companies as well.

Joiner and Spliter

• Convert String List to String and join all the elements by “,”:

    String join = Joiner.on(",").skipNulls().join(Lists.newArrayList("a", "b", null));
    String join2 = Joiner.on(",").useForNull("null").join(Lists.newArrayList("a", "b", null));

in here, we use skipNulls() of Joiner, so if there is null value in the list, this will NOT throw NullPointerException, but you also can use useForNull(String) to replace null value. the second line of code will print “null” instead of skip.

• Split String by “,” and convert into String List

    for(String element : Splitter.on(",").trimResults().omitEmptyStrings().split(" a, , b,, c, ")){
        System.out.println(element);
    }

in here, we split a CSV format of String and convert to String ArrayList, we use omitEmptyString() to skip the empty element and use trimResult() method to remove the blank space before and after the String.

Use CharMatcher

• use CharMatcher to determine Character in a String:

    System.out.println(CharMatcher.is('o').matchesAllOf( "ooo")); //true
    System.out.println(CharMatcher.is('o').matchesAnyOf( "ooo")); //true
    System.out.println(CharMatcher.is('p').matchesAnyOf( "ooo")); //false
    System.out.println(CharMatcher.is('p').matchesNoneOf( "ooo")); //true

• use CharMatcher to determine if String is all digital

    System.out.println(CharMatcher.javaDigit().matchesAllOf("12")); //true 
    System.out.println(CharMatcher.javaDigit().matchesAnyOf("12KD")); //true 

• use CharMatcher to determine the position of Character in String or number of occurrence

    System.out.println(CharMatcher.is('b').indexIn( "abc")); //1
    System.out.println(CharMatcher.is('b').lastIndexIn( "abcb")); //3
    System.out.println(CharMatcher.is('b').countIn( "abcb")); //2

• use CharMatcher to manipulate the String

replace any Character or Character combination with another Charactor

    System.out.println(CharMatcher.anyOf("b").collapseFrom("abcb", '-' )); // return "a-c-"
    System.out.println(CharMatcher.anyOf("bc").collapseFrom("abcbc", '-' )); // return "a--"

replace any String with another String: replace tab with 4 spaces

    rawText = CharMatcher.anyOf("\t").replaceFrom(rawText, "    ")  ;

trim String

    System.out.println(CharMatcher.anyOf("-").trimFrom("abc---")); //return "abc"

Use Bytes/Shorts/Ints/Longs/Floats/Doubles/Chars/Booleans

• use Ints to initialize the Integet List

    List<Integer> list = Ints.asList(1,2,3,4,5);

• use Ints to join Integers into String

    System.out.println(Ints.join("|", 1,2,3,4)); //return "1|2|3|4"

• use Ints to find max and min in array

    System.out.println("max: " + Ints.max(list.stream().mapToInt(e -> e).toArray()));
    System.out.println("max: " + Ints.min(list.stream().mapToInt(e -> e).toArray()));

• use Ints to check if array contains the number

    System.out.println(Ints.contains(list.stream().mapToInt(e -> e).toArray(), 6)); // return false

• use Ints to convert ArrayList to int array

    int[] arr =  Ints.toArray(list);

Use Multiset and Multimap

in Java:

Guava add Multiset to as

Multimap allow you to have duplicate key to avoid the <key, List

    Multimap<String, String> multimap = ArrayListMultimap.create();
    multimap.put("sr", "18");
    multimap.put("sr", "male");

    Collection<String> values = multimap.get("sr"); //return [18, male]

    Multiset<String> multiSet = HashMultiset.create();
    multiSet.add("a");
    multiSet.add("a");
    multiSet.add("b");

    System.out.println("size:" + multiSet.size()); //return 3
    System.out.println("count a:" + multiSet.count("a")); //return 2

Use ImmutableXXX

ImmutableXXX include ImmutableList/ImmutableSet/ImmutableSortedSet/ImmutableMap, here is the example how to implement ImmutableMap

    ImmutableMap<String, String> map = ImmutableMap.of("name", "sr", "age", "18");
    for(String key: map.keySet()){
        System.out.println(("key: " + key + " value: " + map.get(key)));
    }
    //key: name value: sr 
    //key: age  value: 18

Use BiMap

We can use BiMap to reverse lookup: value -> key lookup

    BiMap<String, String> biMap = HashBiMap.create();
    biMap.put("sr", "18");

    System.out.println(biMap.get("sr")); //return 18
    System.out.println(biMap.inverse().get("18")); //return sr