Objects类源码详解（基于jdk1.8.0_261）

1. Objects API概述

• Objects类是一个工具类,包含一系列的静态工具方法;
• 有如下用途: (1) requireNotNull函数要求一个对象不为空,为空则抛异常;
  (2) isNUll和notNULL函数检查一个对象是否为空;
  (3) equals检查两个对象是否相同;
  (4) deepEquals检查两个数据是否完全相同;
  (5) hashCode 返回hash码,hash产生hash码;
  (6) toString 对象toString

2. Objects UML

3. Object源码分析

package java.util;
import java.util.function.Supplier;
public final class Objects {
    private Objects() {
        throw new AssertionError("No java.util.Objects instances for you!");
    }
      //比较a b 两个对象是否相等
    public static boolean equals(Object a, Object b) {
        return (a == b) || (a != null && a.equals(b));
    }
     //比较两个数组各个元素是否相等
    public static boolean deepEquals(Object a, Object b) {
        if (a == b)
            return true;
        else if (a == null || b == null)
            return false;
        else
            return Arrays.deepEquals0(a, b);
    }
    //返回对象o的hashCode
    public static int hashCode(Object o) {
        return o != null ? o.hashCode() : 0;
    }
    //产生values的hashCode
    public static int hash(Object... values) {
        return Arrays.hashCode(values);
    }
      //返回对象o的toString
    public static String toString(Object o) {
        return String.valueOf(o);
    }
      //如果对象不为null,则toString,为空,返回设置的默认nullDefault字符串
    public static String toString(Object o, String nullDefault) {
        return (o != null) ? o.toString() : nullDefault;
    }
     // 根据规则c来比较a b
    public static <T> int compare(T a, T b, Comparator<? super T> c) {
        return (a == b) ? 0 :  c.compare(a, b);
    }
        //为null返回true
    public static boolean isNull(Object obj) {
        return obj == null;
    }
      //不为null 返回true
    public static boolean nonNull(Object obj) {
        return obj != null;
    }
      /**
      *requireNonNull要求obj对象不为null,否则抛NullPointerException
      *
      */
    public static <T> T requireNonNull(T obj) {
        if (obj == null)
            throw new NullPointerException();
        return obj;
    }
    public static <T> T requireNonNull(T obj, String message) {
        if (obj == null)
            throw new NullPointerException(message);
        return obj;
    }
    public static <T> T requireNonNull(T obj, Supplier<String> messageSupplier) {
        if (obj == null)
            throw new NullPointerException(messageSupplier.get());
        return obj;
    }
}

3. Objects示例