java核心技术----Object类
package java.lang;
/**
* Class {@code Object} is the root of the class hierarchy.
* Every class has {@code Object} as a superclass. All objects,
* including arrays, implement the methods of this class.
*
* @author unascribed
* @see java.lang.Class
* @since JDK1.0
*/
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 { }
}
Object类是Java中所有类的始祖，在Java中每个类都是由它扩展而来。
在Java中，只有基本类型不是对象（数组也都扩展了Object类）。
/**
* Created by N3verL4nd on 2016/12/4.
* Object类：所有类的超类
* Object类是不断抽取而来，具备着所有对象都具备的共性内容。
* 常用的共性内容：
* equals toString hashCode clone
*/
class Person{
private int age;
public Person(int age){
this.age = age;
}
}
public class test {
public static void main(String... args) {
Person p1 = new Person(20);
Person p2 = new Person(20);
System.out.println(p1 == p2);
System.out.println(p1.equals(p2));
}
}输出：
false
false
equals比较的是两个对象是否指向同一个位置
重写equals方法：
/**
* Created by N3verL4nd on 2016/12/4.
* Object类：所有类的超类
* Object类似不断抽取而来，具备着所有对象都具备的共性内容。
* 常用的共性内容：
* equals toString hashCode clone
*/
class Person{
private int age;
public Person(int age){
this.age = age;
}
//根据Person类的年龄进行比较
@Override
public boolean equals(Object obj){
if (!(obj instanceof Person)) {
throw new ClassCastException("类型错误");
}
Person p = (Person)obj;
return (age == p.age);
}
}
public class test {
public static void main(String... args) {
Person p1 = new Person(20);
Person p2 = new Person(21);
Person p3 = new Person(20);
System.out.println(p1 == p2);
System.out.println(p1.equals(p2));
System.out.println(p1.equals(p3));
}
}输出：
false
false
true
/**
* Created by N3verL4nd on 2016/12/4.
* Object类：所有类的超类
* Object类似不断抽取而来，具备着所有对象都具备的共性内容。
* 常用的共性内容：
* equals toString hashCode clone
*/
class Person{
private int age;
public Person(int age){
this.age = age;
}
//根据Person类的年龄进行比较
@Override
public boolean equals(Object obj){
if (!(obj instanceof Person)) {
throw new ClassCastException("类型错误");
}
Person p = (Person)obj;
return (age == p.age);
}
}
public class test {
public static void main(String... args) {
Person p1 = new Person(20);
Person p2 = new Person(21);
Person p3 = new Person(20);
Demo demo = new Demo();
System.out.println(p1 == p2);
System.out.println(p1.equals(p2));
System.out.println(p1.equals(p3));
System.out.println("p1 = " + p1);
System.out.println("p1.hashCode() = " + p1.hashCode());
System.out.println("Integer.toHexString(p1.hashCode()) = " + Integer.toHexString(p1.hashCode()));
}
}输出：
| false false true p1 = [email protected] p1.hashCode() = 685325104 Integer.toHexString(p1.hashCode()) = 28d93b30 |
一般重写equals方法后都需要重写HashCode，因为相等的两个对象必须确保hashCode相等。
/**
* Created by N3verL4nd on 2016/12/4.
* Object类：所有类的超类
* Object类似不断抽取而来，具备着所有对象都具备的共性内容。
* 常用的共性内容：
* equals toString hashCode clone
*/
class Person{
private int age;
public Person(int age){
this.age = age;
}
//根据Person类的年龄进行比较
@Override
public boolean equals(Object obj){
if (!(obj instanceof Person)) {
throw new ClassCastException("类型错误");
}
Person p = (Person)obj;
return (age == p.age);
}
@Override
public int hashCode(){
return age;
}
}
public class test {
public static void main(String... args) {
Person p1 = new Person(20);
Person p2 = new Person(21);
Person p3 = new Person(20);
Demo demo = new Demo();
System.out.println(p1 == p2);
System.out.println(p1.equals(p2));
System.out.println(p1.equals(p3));
System.out.println("p1 = " + p1);
System.out.println("p1.hashCode() = " + p1.hashCode());
System.out.println("Integer.toHexString(p1.hashCode()) = " + Integer.toHexString(p1.hashCode()));
}
}/**
* Created by N3verL4nd on 2016/12/4.
* Object类：所有类的超类
* Object类似不断抽取而来，具备着所有对象都具备的共性内容。
* 常用的共性内容：
* equals toString hashCode clone
*/
class Person{
private int age;
public Person(int age){
this.age = age;
}
//根据Person类的年龄进行比较
@Override
public boolean equals(Object obj){
if (!(obj instanceof Person)) {
throw new ClassCastException("类型错误");
}
Person p = (Person)obj;
return (age == p.age);
}
/*
@Override
public int hashCode(){
return age;
}
*/
}
public class test {
public static void main(String... args) {
Person p1 = new Person(20);
System.out.println(p1);
System.out.println(p1.getClass().getName() + "@" + Integer.toHexString(p1.hashCode()));
}
}/**
* Created by N3verL4nd on 2016/12/4.
* Object类：所有类的超类
* Object类似不断抽取而来，具备着所有对象都具备的共性内容。
* 常用的共性内容：
* equals toString hashCode clone
*/
class Person{
private int age;
public Person(int age){
this.age = age;
}
//根据Person类的年龄进行比较
@Override
public boolean equals(Object obj){
if (!(obj instanceof Person)) {
throw new ClassCastException("类型错误");
}
Person p = (Person)obj;
return (age == p.age);
}
/*
@Override
public int hashCode(){
return age;
}
*/
public String toString(){
return "[email protected]@" + age;
}
}
public class test {
public static void main(String... args) {
Person p1 = new Person(20);
System.out.println(p1);
System.out.println(p1.getClass().getName() + "@" + Integer.toHexString(p1.hashCode()));
}
}输出：
[email protected]@20
[email protected]