[英]Java Guava filter two collection with different type
I have two collection: 我有两个收藏:
ArrayList<B> currentB = new ArrayList<B>();
{
currentB.add(new B(new A("1")));
currentB.add(new B(new A("2")));
currentB.add(new B(new A("7")));
currentB.add(new B(new A("3")));
currentB.add(new B(new A("4")));
}
ArrayList<A> newA = new ArrayList<A>();
{
newA.add(new A("1"));
newA.add(new A("5"));
newA.add(new A("2"));
newA.add(new A("6"));
newA.add(new A("7"));
newA.add(new A("8"));
}
Collections has following types: 集合具有以下类型:
class A {
private String id;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
A nodeRef = (A) o;
return !(id != null ? !id.equals(nodeRef.id) : nodeRef.id != null);
}
public A() {
}
public A(String id) {
this.id = id;
}
@Override
public String toString() {
return "NodeRef{" +
"id='" + id + '\'' +
'}';
}
}
class B {
private A a;
public A a() {
return a;
}
public A getA() {
return a;
}
public void setA(A a) {
this.a = a;
}
@Override
public String toString() {
return "B{" +
"a=" + a +
'}';
}
public B(A a) {
this.a = a;
}
public B() {
}
}
I want to create (the best result is modify newA and currentB) two list: 我要创建(最好的结果是修改newA和currentB)两个列表:
I can do it with guava, but it need to create 3 collection: 我可以用番石榴做,但需要创建3个集合:
Function<B, A> BtoA = new Function<B, A>() {
public A apply(final B b) {
return b.getA();
}
};
Collection<A> currentA = Collections2.transform(currentB, BtoA);
java.util.Collection<A> idToDelete = Collections2.filter(currentA, Predicates.not(Predicates.in(newA)));
java.util.Collection<A> idToAdd = Collections2.filter(newA, Predicates.not(Predicates.in(currentA)));
System.out.println("Old B" + idToDelete);
System.out.println("New A" + idToAdd);
Is there a way to get rid of Collection.transform or even the best way? 有没有办法摆脱Collection.transform甚至最好的办法?
It will look quite nice with java 8 streams API: 使用Java 8 Streams API看起来会很好:
java.util.Collection<String> idToDelete =
currentB.stream() //get the stream
.filter(b -> !newA.contains(b.getA())) // filter those b, whose A is in newA
.map(b -> b.getA().id) // map transform to get just an Id (you can use just getA() here)
.collect(Collectors.toList()); // finally transform back to list
java.util.Collection<String> idToAdd =
newA.stream() // again get stream
.filter(
// this is a little bit fancy...
// only leave those A, for which currentB doesn't contain element, that has getA() equals to that A
a -> currentB.stream().noneMatch(
b -> b.getA().equals(a)
)
)
.map(a -> a.id) // again get id
.collect(Collectors.toList()); // transform to list
[EDIT:] [编辑:]
If you look into guava's source code, you can see, that transform
just wraps your existing one with a transform function. 如果查看番石榴的源代码,您会看到,该transform
只是将现有的转换与转换功能包装在一起。 So guava basically works just as java 8 streams. 因此,番石榴基本上就像Java 8流一样工作。 So you can actually use transform as you did. 因此,您实际上可以像以前一样使用transform。 If absolutely don't wanna do it, this is complete example with guava: 如果绝对不想这样做,这是番石榴的完整示例:
Function<B, A> BtoA = new Function<B, A>() {
public A apply(final B b) {
return b.getA();
}
};
Function<A, String> aToId = new Function<A, String>() {
public String apply(final A a) {
return a.getId();
}
};
java.util.Collection<B> bToDelete = Collections2.filter(currentB, Predicates.compose(Predicates.not(Predicates.in(newA)), BtoA));
//without transform, looks ugly
java.util.Collection<A> aToAdd = Collections2.filter(newA, new Predicate<A>() {
@Override
public boolean apply(final A a) {
return !Iterables.any(currentB, new Predicate<B>() {
@Override
public boolean apply(B b) {
return b.getA().equals(a);
}
});
}
});
// this is essentially the same, you can safely use transform
//java.util.Collection<A> aToAdd = Collections2.filter(newA, Predicates.not(Predicates.in(Collections2.transform(currentB, BtoA))));
java.util.Collection<String> idToDelete = Collections2.transform(bToDelete, Functions.compose(aToId, BtoA));
java.util.Collection<String> idToAdd = Collections2.transform(aToAdd, aToId);
System.out.println("Old B: " + idToDelete);
System.out.println("New A: " + idToAdd);
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