guava

主要翻译GUAVA的介绍

1. 过滤数据，数据验证器

• 通常
  

  public Car(Engine engine) {
  this.engine = checkNotNull(engine); // NPE
  }
  public void drive(double speed) {
  checkArgument(speed > 0.0,
  "speed (%s) must be positive", speed); // IAE
  checkState(engine.isRunning(),
  "engine must be running"); // ISE
  ...
  }

   在上面需要检查 speed，engine

• return Objects.toStringHelper(this)
  .add("name", name)
  .add("id", userId)
  .add("pet", petName) // petName is @Nullable!
  .omitNullValues()
  .toString();
  // "Person{name=Kurt Kluever, id=42}"
  Or without .omitNullValues():  omitNullValues()函数可以过滤空的数据
  // "Person{name=Kurt Kluever, id=42, pet=null}"   
  

这个特性，很适合做数据清洗，要比apache的validator方便；validator可以是一个事件驱动方式工作，而guava更像是annotation方式工作。

 

2. String JOIN，Split

 

Joiner concatenates strings using a delimiter
● throws a NPE on null objects, unless:
○ .skipNulls()
○ .useForNull(String)
private static final Joiner JOINER =
Joiner.on(", ").skipNulls();
JOINER.join("Kurt", "Kevin", null, "Chris");
// yields: "Kurt, Kevin, Chris"

 这join 不如apache的collections和apache的commons-lang库，apache的join和split更强大。唯一区别是，apache仍然是原有的JAVA风格；而这个像脚本风格，或者注释风格。

 

1. Functional Programming

Function<F, T>
○ one way transformation of F into T
○ T apply(F input)
○ most common use: transforming collections (view)
Predicate<T>
○ determines true or false for a given T
○ boolean apply(T input)
○ most common use: filtering collections (view)

 

这个也与apache common中的factory库相似

private static final Predicate<Client> ACTIVE_CLIENT =
new Predicate<Client>() {
public boolean apply(Client client) {
return client.activeInLastMonth();
}
};
// Returns an immutable list of the names of
// the first 10 active clients in the database.
FluentIterable.from(database.getClientList())
.filter(ACTIVE_CLIENT)
.transform(Functions.toStringFunction())
.limit(10)
.toList();

 

FluentIterable API
● Chaining (returns FluentIterable)
○ skip
○ limit
○ cycle
○ filter, transform
● Querying (returns boolean)
○ allMatch, anyMatch
○ contains, isEmpty
● Converting
○ to{List, Set, SortedSet}
○ toArray
● Extracting
○ first, last, firstMatch (returns
Optional<E>)
○ get (returns E)

 

 

1. TABLE

这个不错

Table<R, C, V>
A "two-tier" map, or a map with two keys (called the "row key"
and "column key").
● can be sparse or dense
○ HashBasedTable: uses hash maps (sparse)
○ TreeBasedTable: uses tree maps (sparse)
○ ArrayTable: uses V[][] (dense)
● many views on the underlying data are possible
○ row or column map (of maps)
○ row or column key set
○ set of all cells (as <R, C, V> entries)
● use instead of Map<R, Map<C, V>>