java8之默认接口实现

本是古典何须时尚 2022-02-25 03:07 173阅读 0赞

### java8之默认接口实现 ###

*   *  简介
     *  Predicate源码
     *  代码演示
     *  冲突解决
 *  自我推荐

## 简介 ##

**定义：申明方法的同时提供实现**

1.  允许在接口内声明静态方法
2.  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 ##

1.  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)
2.  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
3.  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

# 自我推荐 #

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