All classes ancestor class Object class and Objects

class Object（java.lang）

Note: The ancestor class of all Java classes.

private static native void registerNatives();

static {
    registerNatives();
}

• Defines registerNatives native method, register the class implement all the native methods in addition to the method

  • native keyword modified method is called localization method is to contact the Java program and the underlying host operating system connection method

• Method calls the method to register the local static static block of code, the local implementation of the registration process action

  • After the class is loaded, convenient to call localization method, without caring about the realization of the principle underlying

  • If the native method implementation is modified, can be achieved by re-calling reload the updated local registration method

public final native Class<?> getClass();

• Acquiring the actual type of the object instance in memory

Example 1: acquiring the actual type of the object

Object obj = new Date();
System.out.println("实例对象实际类型：" + obj.getClass().getName());
//输出结果：实例对象实际类型：java.util.Date

public native int hashCode();

• hash code value object class instance, the value is a value based on certain rules related to the object information maps into.
• Because different values ​​for different hash code of an object instance, can be judged by comparing the hash code value for the same object is a target object.

public boolean equals(Object obj) {
    return (this == obj);
}

• Compare the current object and incoming objects for equality and returns true if equal, otherwise false.
• "==" to compare two objects address in memory are the same. In practice, some classes had to rewrite this method, for example: String class, Math class.

protected native Object clone() throws CloneNotSupportedException;

public interface Cloneable {}

• Quickly create a copy of an object (clone).
• The method was modified protected keywords, so the class must inherit from the Object class, and implement the Cloneable interface to use. Otherwise it will throw an exception CloneNotSupportedException.
• A copy of the original object is not a reference to the object, but creates a new object of the same content.
• Although Cloneable interface does not define any method, but must be implemented when the object cloning.

Example 2: Cloning of the object Jane

public class MyClone implements Cloneable {
	
	private String name;
	
	public MyClone(String name) {
		this.name = name;
	}
    
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
    
	@Override
	protected Object clone() throws CloneNotSupportedException {
		return super.clone();
	}

	public static void main(String[] args) throws CloneNotSupportedException {
		MyClone obj = new MyClone("小明");
		MyClone obj1 = (MyClone) obj.clone();
		System.out.println("两个对象是否同一个对象：" + obj.equals(obj1));
        //输出结果：两个对象是否同一个对象：false
        System.out.println("克隆对象名称：" + obj1.getName());
        //输出结果：克隆对象名称：小明
	}

}

public String toString() {
    return getClass().getName() + "@" + Integer.toHexString(hashCode());
}

• Gets a string representation of the object, the default is "class full path name @ hexadecimal representation of the hash code value."

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);
}

• notify and notifyAll methods used to wake up processes waiting on this object's monitor.
• The method used to set the thread wait wait. To milliseconds timeout denotes the wait, nanos nanoseconds represents the value of the additional wait (in the range between 0 to 999999).

protected void finalize() throws Throwable { }

• Garbage collector ready to release memory when will first call finalize method.

final class Objects（java.util）

Note: This class is final, and its constructor is private. This class represents the other classes can not be inherited or modified.

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);
}

//Arrays.deepEquals0方法
static boolean deepEquals0(Object e1, Object e2) {
    assert e1 != null;
    boolean eq;
    if (e1 instanceof Object[] && e2 instanceof Object[])
        eq = deepEquals ((Object[]) e1, (Object[]) e2);
    else if (e1 instanceof byte[] && e2 instanceof byte[])
        eq = equals((byte[]) e1, (byte[]) e2);
    else if (e1 instanceof short[] && e2 instanceof short[])
        eq = equals((short[]) e1, (short[]) e2);
    else if (e1 instanceof int[] && e2 instanceof int[])
        eq = equals((int[]) e1, (int[]) e2);
    else if (e1 instanceof long[] && e2 instanceof long[])
        eq = equals((long[]) e1, (long[]) e2);
    else if (e1 instanceof char[] && e2 instanceof char[])
        eq = equals((char[]) e1, (char[]) e2);
    else if (e1 instanceof float[] && e2 instanceof float[])
        eq = equals((float[]) e1, (float[]) e2);
    else if (e1 instanceof double[] && e2 instanceof double[])
        eq = equals((double[]) e1, (double[]) e2);
    else if (e1 instanceof boolean[] && e2 instanceof boolean[])
        eq = equals((boolean[]) e1, (boolean[]) e2);
    else
        eq = e1.equals(e2);
    return eq;
}

• The method determines whether the two are equal two objects. If the object is an array, using deepEquals depth comparison method.

public static int hashCode(Object o) {
    return o != null ? o.hashCode() : 0;
}

public static int hash(Object... values) {
    return Arrays.hashCode(values);
}

//Arrays.hashCode
public static int hashCode(Object a[]) {
    if (a == null)
        return 0;

    int result = 1;

    for (Object element : a)
        result = 31 * result + (element == null ? 0 : element.hashCode());

    return result;
}

• and hashCode method for obtaining an object hash value hash code or a collection of objects. If the object is null, 0 is returned.
• The hash code value array of objects (result = 31 * result + single object hash code value).

public static String toString(Object o) {
    return String.valueOf(o);
}

public static String toString(Object o, String nullDefault) {
    return (o != null) ? o.toString() : nullDefault;
}

• Get string representing the object, if the object is empty, can be passed through the second return parameter to set the default string.

public static <T> int compare(T a, T b, Comparator<? super T> c) {
    return (a == b) ? 0 :  c.compare(a, b);
}

• By the comparator is provided to compare the size of two objects, for the same object if the two objects, 0 is returned.

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;
}

• Determining whether the object is empty, if it is empty, then a NullPointerException exception abnormality content settings. If empty, the original object is returned.

public static boolean isNull(Object obj) {
    return obj == null;
}

public static boolean nonNull(Object obj) {
    return obj != null;
}

• Determine whether the object is empty.