很有趣的一个抽象类。
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public abstract class Either<L, R> implements Serializable{/** * */private static final long serialVersionUID = 0l;private Either() { }@SuppressWarnings("unchecked")public boolean isLeft() {return (this instanceof Left);}@SuppressWarnings("unchecked")public boolean isRight() {return (this instanceof Right);}public abstract L _left();public abstract R _right();public static <L, R> Either<L, R> right(final R r) {return new Right<L, R>(r);}public static <L, R> Either<L, R> left(final L l) {return new Left<L, R>(l);}private static final class Left<L, R> extends Either<L, R> implements Serializable{/** * */private static final long serialVersionUID = 7066970081776250327L;private final L l;Left(final L l) {this.l = l;}@Overridepublic L _left() {return l;}@Overridepublic R _right() {return null;}}private static final class Right<L, R> extends Either<L, R> implements Serializable{/** * */private static final long serialVersionUID = -894488879249418100L;private final R r;Right(final R r) {this.r = r;}@Overridepublic L _left() {return null;}@Overridepublic R _right() {return r;}}}?
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要么 left，要么right，哈哈.不能继承的。。。。