java8之默认接口实现
简介
定义:申明方法的同时提供实现
- 允许在接口内声明静态方法
- 指定接口方法的默认实现
Predicate源码
/*
* Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.util.function;
import java.util.Objects;
/**
1. Represents a predicate (boolean-valued function) of one argument.
2. 3. <p>This is a <a href="package-summary.html">functional interface</a>
4. whose functional method is {@link #test(Object)}.
5. 6. @param <T> the type of the input to the predicate
7. 8. @since 1.8
*/
@FunctionalInterface
public interface Predicate<T> {
/**
* Evaluates this predicate on the given argument.
*
* @param t the input argument
* @return {@code true} if the input argument matches the predicate,
* otherwise {@code false}
*/
boolean test(T t);
/**
* Returns a composed predicate that represents a short-circuiting logical
* AND of this predicate and another. When evaluating the composed
* predicate, if this predicate is {@code false}, then the {@code other}
* predicate is not evaluated.
*
* <p>Any exceptions thrown during evaluation of either predicate are relayed
* to the caller; if evaluation of this predicate throws an exception, the
* {@code other} predicate will not be evaluated.
*
* @param other a predicate that will be logically-ANDed with this
* predicate
* @return a composed predicate that represents the short-circuiting logical
* AND of this predicate and the {@code other} predicate
* @throws NullPointerException if other is null
*/
default Predicate<T> and(Predicate<? super T> other) { //接口方法的默认实现
Objects.requireNonNull(other);
return (t) -> test(t) && other.test(t);
}
/**
* Returns a predicate that represents the logical negation of this
* predicate.
*
* @return a predicate that represents the logical negation of this
* predicate
*/
default Predicate<T> negate() { //接口方法的默认实现
return (t) -> !test(t);
}
/**
* Returns a composed predicate that represents a short-circuiting logical
* OR of this predicate and another. When evaluating the composed
* predicate, if this predicate is {@code true}, then the {@code other}
* predicate is not evaluated.
*
* <p>Any exceptions thrown during evaluation of either predicate are relayed
* to the caller; if evaluation of this predicate throws an exception, the
* {@code other} predicate will not be evaluated.
*
* @param other a predicate that will be logically-ORed with this
* predicate
* @return a composed predicate that represents the short-circuiting logical
* OR of this predicate and the {@code other} predicate
* @throws NullPointerException if other is null
*/
default Predicate<T> or(Predicate<? super T> other) { //接口方法的默认实现
Objects.requireNonNull(other);
return (t) -> test(t) || other.test(t);
}
/**
* Returns a predicate that tests if two arguments are equal according
* to {@link Objects#equals(Object, Object)}.
*
* @param <T> the type of arguments to the predicate
* @param targetRef the object reference with which to compare for equality,
* which may be {@code null}
* @return a predicate that tests if two arguments are equal according
* to {@link Objects#equals(Object, Object)}
*/
static <T> Predicate<T> isEqual(Object targetRef) { //静态方法
return (null == targetRef)
? Objects::isNull
: object -> targetRef.equals(object);
}
}
代码演示
public interface A {
//默认接口实现
default void hello(){
System.out.println("Hello World");
}
//静态方法
static void say(){
System.out.println("Hello World");
}
}
冲突解决
- 类中的方法优先级最高(类或父类中声明的方法优先于任何声明为默认方法的优先级)
- 如果无法依据第一条,那么子接口优先级更高:函数签名相同时,优先选择拥有最具体实现的默认方法的接口,如果B继承了A,那么B就比A更加具体
- 继承了多个接口的类必须通过显示覆盖和调用期望的方法