Guava 中针对集合的 filter 和过滤功能

@Test  

public  void whenFilterWithIterables_thenFiltered() {  

 List<String> names = Lists.newArrayList("John", "Jane", "Adam", "Tom");  

 Iterable<String> result = Iterables.filter(names, Predicates.containsPattern("a"));  

   

 assertThat(result, containsInAnyOrder("Jane", "Adam"));  

}  

@Test  

public  void whenFilterWithCollections2_thenFiltered() {  

 List<String> names = Lists.newArrayList("John", "Jane", "Adam", "Tom");  

 Collection<String> result = Collections2.filter(names, Predicates.containsPattern("a"));  

       

 assertEquals(2, result.size());  

 assertThat(result, containsInAnyOrder("Jane", "Adam"));  

   

 result.add("anna");  

 assertEquals(5, names.size());  

}  

@Test  

public  void whenFilterCollectionWithCustomPredicate_thenFiltered() {  

 Predicate<String> predicate =  new Predicate<String>() {  

 @Override  

 public boolean apply(String input) {  

 return input.startsWith("A") || input.startsWith("J");  

 }  

 };  

   

 List<String> names = Lists.newArrayList("John", "Jane", "Adam", "Tom");  

 Collection<String> result = Collections2.filter(names, predicate);  

   

 assertEquals(3, result.size());  

 assertThat(result, containsInAnyOrder("John", "Jane", "Adam"));  

}  

@Test  

public  void whenTransformWithIterables_thenTransformed() {  

 Function<String, Integer> function =  new Function<String, Integer>() {  

 @Override  

 public Integer apply(String input) {  

 return input.length();  

 }  

 };  

   

 List<String> names = Lists.newArrayList("John", "Jane", "Adam", "Tom");  

 Iterable<Integer> result = Iterables.transform(names, function);  

   

 assertThat(result, contains(4, 4, 4, 3));  

}  

@Test  

public  void whenTransformingUsingComposedFunction_thenTransformed() {  

 Function<String,Integer> f1 =  new Function<String,Integer>(){  

 @Override  

 public Integer apply(String input) {  

 return input.length();  

 }  

 };  

   

 Function<Integer,Boolean> f2 =  new Function<Integer,Boolean>(){  

 @Override  

 public Boolean apply(Integer input) {  

 return input %  2  ==  0;  

 }  

 };  

   

 List<String> names = Lists.newArrayList("John", "Jane", "Adam", "Tom");  

 Collection<Boolean> result = Collections2.transform(names, Functions.compose(f2, f1));  

   

 assertEquals(4, result.size());  

 assertThat(result, contains(true, true, true, false));  

}  

@Test  

public  void whenFilteringAndTransformingCollection_thenCorrect() {  

 Predicate<String> predicate =  new Predicate<String>() {  

 @Override  

 public boolean apply(String input) {  

 return input.startsWith("A") || input.startsWith("T");  

 }  

 };  

   

 Function<String, Integer> func =  new Function<String,Integer>(){  

 @Override  

 public Integer apply(String input) {  

 return input.length();  

 }  

 };  

   

 List<String> names = Lists.newArrayList("John", "Jane", "Adam", "Tom");  

 Collection<Integer> result = FluentIterable.from(names)  

 .filter(predicate)  

 .transform(func)  

 .toList();  

   

 assertEquals(2, result.size());  

 assertThat(result, containsInAnyOrder(4, 3));  

}
​