LongUnaryOperator.java

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package java.util.function;

import java.util.Objects;

/**
 * Represents an operation on a single {@code long}-valued operand that produces
 * a {@code long}-valued result.  This is the primitive type specialization of
 * {@link UnaryOperator} for {@code long}.
 *
 * <p>This is a <a href="package-summary.html">functional interface</a>
 * whose functional method is {@link #applyAsLong(long)}.
 *
 * @see UnaryOperator
 * @since 1.8
 */
/*
 * 函数式接口：LongUnaryOperator
 *
 * long一元操作
 *
 * 参数：long
 * 返回：long
 */
@FunctionalInterface
public interface LongUnaryOperator {
    
    /**
     * Applies this operator to the given operand.
     *
     * @param operand the operand
     *
     * @return the operator result
     */
    long applyAsLong(long operand);
    
    /**
     * Returns a unary operator that always returns its input argument.
     *
     * @return a unary operator that always returns its input argument
     */
    // 标识转换
    static java.util.function.LongUnaryOperator identity() {
        return t -> t;
    }
    
    /**
     * Returns a composed operator that first applies the {@code before}
     * operator to its input, and then applies this operator to the result.
     * If evaluation of either operator throws an exception, it is relayed to
     * the caller of the composed operator.
     *
     * @param before the operator to apply before this operator is applied
     *
     * @return a composed operator that first applies the {@code before}
     * operator and then applies this operator
     *
     * @throws NullPointerException if before is null
     * @see #andThen(java.util.function.LongUnaryOperator)
     */
    // f1.compose(f2)：先执行f2，再执行f1
    default java.util.function.LongUnaryOperator compose(java.util.function.LongUnaryOperator before) {
        Objects.requireNonNull(before);
        return (long v) -> applyAsLong(before.applyAsLong(v));
    }
    
    /**
     * Returns a composed operator that first applies this operator to
     * its input, and then applies the {@code after} operator to the result.
     * If evaluation of either operator throws an exception, it is relayed to
     * the caller of the composed operator.
     *
     * @param after the operator to apply after this operator is applied
     *
     * @return a composed operator that first applies this operator and then
     * applies the {@code after} operator
     *
     * @throws NullPointerException if after is null
     * @see #compose(java.util.function.LongUnaryOperator)
     */
    // f1.andThen(f2)：先执行f1，再执行f2
    default java.util.function.LongUnaryOperator andThen(java.util.function.LongUnaryOperator after) {
        Objects.requireNonNull(after);
        return (long t) -> after.applyAsLong(applyAsLong(t));
    }
}