常用类之Object

public class TestObject1 {

public static void main(String[] args) {
//hashCode是根据对象的内部地址再转换的一个整数
Student s1 = new Student();
System.out.println(s1.hashCode());

Student s2 = new Student();
System.out.println(s2.hashCode());

//由于hashCode是根据对象的内部地址转换的，把s1的引用付给了s3，s1跟s3地址一样，hashCode也一样
Student s3 = s1;
System.out.println(s3.hashCode());

}
}

353591321
722080798
353591321

public class TestObject1 {

public static void main(String[] args) {
Student s = new Student();
//返回运行时类
Class c = s.getClass();
System.out.println(c.getName());

}
}

public class TestObject1 {

public static void main(String[] args) {
Human human = new Human();

System.out.println(human.hashCode());
System.out.println(human.getClass().getName());
//将对象转换为字符串。如果不重写，默认是getClass().getName()+@+Integer.toHexString(hashCode());
System.out.println(human.getClass().getName()+"@"+Integer.toHexString(human.hashCode()));
System.out.println(human.toString());

//直接输出对象。也就是输出human.toString()方法
System.out.println(human);
}
}

258702862
cn.eminem_07.Human
cn.eminem_07.Human@f6b7e0e
cn.eminem_07.Human@f6b7e0e

cn.eminem_07.Human@f6b7e0e

public class TestObject1 {

public static void main(String[] args) {

Human h3 = h1;
// 比较的是引用类型
System.out.println(h1 == h2);
// equals如果不重写，默认比较的是对象的引用地址
System.out.println(h1.equals(h2));

System.out.println(h1.equals(h3));
}
}

false
false
true

public class Human {

private int age;
private String name;

public Human() {
super();
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public Human(int age, String name) {
super();
this.age = age;
this.name = name;
}

@Override
public String toString() {
return "Human [age=" + age + ", name=" + name + "]";
}

@Override
public boolean equals(Object obj) {
Human s = (Human) obj;
//equal 默认是比较对象，这边重写比较对象的属性值
if(this.name.equals(s.name) && this.age == s.age){
return true;
}else{
return false;
}
}

}

false
false
true

package cn.eminem_08;

public class Human {

private int age;
private String name;

public Human() {
super();
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public Human(int age, String name) {
super();
this.age = age;
this.name = name;
}

@Override
public String toString() {
return "Human [age=" + age + ", name=" + name + "]";
}

@Override
public boolean equals(Object obj) {

//同一对象没必要比较
if(this == obj){
return true;
}

//判断obj是不是Human类，不是Human类，没必要向下转型再比较、
//使用instanceof 判断对象是否是某个类
if(!(obj instanceof Human)){
return false;
}

Human s = (Human) obj;
System.out.println("同一对象，还需要向下转型进行比较吗？");
return this.name.equals(s.name) && this.age == s.age;
}

}

public class TestObject1 {

public static void main(String[] args) {

Human h1 = new Human(1,"zs");
Human h2 = new Human(1,"zs");
Human h3 = h1;
Human h4 = new Human(1,"ls");

// 比较的是引用类型
System.out.println(h1 == h2);

// 不是同一个对象 equals如果不重写，默认比较的是对象的引用地址
System.out.println(h1.equals(h2));

//是同一对象
System.out.println(h1.equals(h3));

//不是同一个对象
System.out.println(h1.equals(h4));
}
}

false
同一对象，还需要向下转型进行比较吗？
true
true
同一对象，还需要向下转型进行比较吗？
false

public class TestObject1 {

public static void main(String[] args) throws CloneNotSupportedException {

Human h = new Human();
//克隆新对象obj
Object obj = h.clone();

Human h2 = (Human) obj;
}
}

Cloneable

Object.clone()

package cn.eminem_09;

public class Human implements Cloneable{

private int age;
private String name;

public Human() {
super();
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public Human(int age, String name) {
super();
this.age = age;
this.name = name;
}

@Override
public String toString() {
return "Human [age=" + age + ", name=" + name + "]";
}

@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
}

public class TestObject1 {

public static void main(String[] args) throws CloneNotSupportedException {

Human h = new Human(1, "zs");
// 克隆新对象obj
Object obj = h.clone();

Human h2 = (Human) obj;

Human h3 = h;

System.out.println(h.getName());
System.out.println(h2.getName());
System.out.println(h3.getName());

System.out.println("-----------");

h3.setName("ls");
//
System.out.println(h.getName());
System.out.println(h2.getName());
//由于h3跟h1引用同一对象，h3.name改变，h1.name也改变。但是克隆的对象不变
//也就是说clone出来的是新对象。地址值不一样
System.out.println(h3.getName());

}