一、Object 类

如果一个类没有指定父类，默认就是继承 Object 类。Object 类里面共有 11 个方法：经常用到的 equals()，toString() 都是直接使用或者重写 Object 里面的这些方法；另外还有 final native 修饰的方法：反射需要用到的 getClass()，线程操作需要的 notify()，notifyAll()，wait(long timeout)；还有 native 修饰的方法：hashCode() 和 clone()

源码：

package java.lang;public class Object {private static native void registerNatives();static {registerNatives();}public final native Class<?> getClass();public native int hashCode();public boolean equals(Object obj) {return (this == obj);}protected native Object clone() throws CloneNotSupportedException;public String toString() {return getClass().getName() + "@" + Integer.toHexString(hashCode());}public final native void notify();public final native void notifyAll();public final native void wait(long timeout) throws InterruptedException;public final void wait(long timeout, int nanos) throws InterruptedException {if (timeout < 0) {throw new IllegalArgumentException("timeout value is negative");}if (nanos < 0 || nanos > 999999) {throw new IllegalArgumentException("nanosecond timeout value out of range");}if (nanos > 0) {timeout++;}wait(timeout);}public final void wait() throws InterruptedException {wait(0);}protected void finalize() throws Throwable { }
}

二、Objects 类

Objects 类是 final 修饰的类，不可继承，内部方法都是 static 方法，从 jdk1.7 开始才引入了 Objects 类。

源码：

package java.util;import java.util.function.Supplier;public final class Objects {private Objects() {throw new AssertionError("No java.util.Objects instances for you!");}public static boolean equals(Object a, Object b) {return (a == b) || (a != null && a.equals(b));}public static boolean deepEquals(Object a, Object b) {if (a == b)return true;else if (a == null || b == null)return false;elsereturn Arrays.deepEquals0(a, b);}public static int hashCode(Object o) {return o != null ? o.hashCode() : 0;}public static int hash(Object... values) {return Arrays.hashCode(values);}public static String toString(Object o) {return String.valueOf(o);}public static String toString(Object o, String nullDefault) {return (o != null) ? o.toString() : nullDefault;}public static <T> int compare(T a, T b, Comparator<? super T> c) {return (a == b) ? 0 :  c.compare(a, b);}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 boolean isNull(Object obj) {return obj == null;}public static boolean nonNull(Object obj) {return obj != null;}public static <T> T requireNonNull(T obj, Supplier<String> messageSupplier) {if (obj == null)throw new NullPointerException(messageSupplier.get());return obj;}
}

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Object 和 Objects 的区别

一、Object 类

二、Objects 类

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