Google Guava学习之Constraint

import java.util.HashSet;
import java.util.Set;
import com.google.common.base.Objects;
import com.google.common.collect.Constraint;
import com.google.common.collect.Constraints;
import com.google.common.collect.Sets;

public class TryConstraint {
// create a class A
public static class A {
private int a;
public A(int a) {
this.a = a;
}
public int getA() {
return this.a;
}
@Override
public String toString() {
return String.format("[a=%d]", this.a);
}
@Override
public boolean equals(Object obj) {
if (obj != null || !(obj instanceof A)) {
return false;
} else {
A aA = (A)obj;
return aA.a == this.a;
}
}
@Override
public int hashCode() {
return Objects.hashCode(this.a);
}
}
public static void main(String[] args) {
// Create a specified constraint
Constraint<A> aConstraint = new Constraint<TryConstraint.A>() {
@Override
public A checkElement(A aA) {
if (aA == null) {
throw new NullPointerException();
}
if (aA.getA() % 2 == 0) {
throw new RuntimeException("Can't be even");
}
return aA;
}
};
HashSet<A> aSet = Sets.newHashSet(new A(0), new A(1), new A(2), new A(3));
// Returns a constrained view of the specified set, using the specified constraint.
// Any operations that add new elements to the set will call the provided constraint.
// However, this method does not verify that existing elements satisfy the constraint.
Set<A> newSet = Constraints.constrainedSet(aSet, aConstraint);
System.out.println(newSet); // [[a=3], [a=1], [a=2], [a=0]]
newSet.add(new A(5));
newSet.add(new A(5));
System.out.println(newSet); // [[a=3], [a=1], [a=2], [a=5], [a=5], [a=0]]
newSet.add(null);
System.out.println(newSet); // will throw NullPointerException
newSet.add(new A(6));
System.out.println(newSet); // will throw RuntimeException
}
}