深入瞭解Java核心類庫–Objects類

package java.util;
import jdk.internal.util.Preconditions;
import jdk.internal.vm.annotation.ForceInline;
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;
        else
            return 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 requireNonNullElse(T obj, T defaultObj) {
        return (obj != null) ? obj : requireNonNull(defaultObj, "defaultObj");
    }
    public static <T> T requireNonNullElseGet(T obj, Supplier<? extends T> supplier) {
        return (obj != null) ? obj
                : requireNonNull(requireNonNull(supplier, "supplier").get(), "supplier.get()");
    }
    public static <T> T requireNonNull(T obj, Supplier<String> messageSupplier) {
        if (obj == null)
            throw new NullPointerException(messageSupplier == null ?
                                           null : messageSupplier.get());
        return obj;
    }
    @ForceInline
    public static
    int checkIndex(int index, int length) {
        return Preconditions.checkIndex(index, length, null);
    }
    public static int checkFromToIndex(int fromIndex, int toIndex, int length) {
        return Preconditions.checkFromToIndex(fromIndex, toIndex, length, null);
    }
    public static int checkFromIndexSize(int fromIndex, int size, int length) {
        return Preconditions.checkFromIndexSize(fromIndex, size, length, null);
    }
}

public static void main(String[] args){
	String text = "123";
	say(text);
	int a = 10;
	say(a);
	say("123");
}
public static void say(Object o){//多態的體現
	System.out.println(o);
}

public static void main(String[] args) {
        Person p = new Person(1234,"張三");
        Person e = new Person(2345,"李四");
        System.out.println("p:"+p.hashCode());//p:1239731077
        System.out.println("e:"+e.hashCode());//e:357863579
        System.out.println(p.equals(e));//false
        e=p;//此時指向相同的內存地址
        System.out.println("e:"+e.hashCode());//e:1239731077
        System.out.println(p.equals(e));//true
}

public static void main(String[] args) {
        Person p = new Person(1234,"張三");
        Person e = new Person(2345,"李四");
        System.out.println("e.getClass()："+e.getClass());
        System.out.println("e.hashCode()："+e.hashCode());
        System.out.println("e.toString()："+e.toString());
}

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