Object类
- 超类、基类,所有类的直接或间接父类,处于继承树的最顶层
- 任何类,如果没有书写extends显示继承某个类,都默认直接继承Object类,否则为间接继承
- Object类中所定义的方法,是所有对象都具备的方法
- Object类型可以存储任何对象
- 作为参数,可接受任何对象
- 作为返回值,可返回任何对象
getClass()方法
- public final Class<?> getClass(){}
- 返回引用储存的实际对象类型
- 应用:通常用于判断两个引用中实际储存对象类型是否一致
package object;
public class Student {
private String name;
private int age;
public Student() {
}
public Student(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
package object;
public class TestStudent {
public static void main(String[] args) {
Student student1 = new Student("aaa",18);
Student student2 = new Student("bbb",20);
//判断1和2是不是同一个类型
Class class1=student1.getClass();
Class class2=student2.getClass();
if (class1==class2){
System.out.println("属于同一个类型");
}else{
System.out.println("不是同一个类型");
}
}
}
hashCode()方法
- public int hashCode(){}
- 返回该对象的哈希码值
- 哈希值根据对象的地址或字符串或数字使用hash算法计算出来的int类型的数值
- 一般情况下相同对象返回相同哈希码
package object;
public class Student {
private String name;
private int age;
public Student() {
}
public Student(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
package object;
public class TestStudent {
public static void main(String[] args) {
Student student1 = new Student("aaa",18);
Student student2 = new Student("bbb",20);
//hashCode方法
System.out.println(student1.hashCode());
System.out.println(student2.hashCode());
Student student3=student1;
System.out.println(student3.hashCode());
}
}
toString()方法
- public String toString(){}
- 返回该对象的字符串表示(表现形式)
- 可以根据程序需求覆盖方法,如:展示对象各个属性值
package object;
public class Student {
private String name;
private int age;
public Student() {
}
public Student(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Student{name=" + name + " , age=" +age + "}";
}
}
package object;
public class TestStudent {
public static void main(String[] args) {
//toString方法
System.out.println(student1.toString());
System.out.println(student2.toString());
}
}
equals()方法
- public boolean equals(Object obj){}
- 默认实现为(this==obj),比较两个对象地址是否相等
- 可进行覆盖,比较两个对象的内容是否相同
- 覆盖步骤
- 比较两个引用是否指向同一个对象
- 判断obj是否为null
- 强制类型转换
- 依次比较各个属性值是否相等
- 覆盖步骤
package object;
import com.sun.org.apache.xpath.internal.objects.XObject;
public class Student {
private String name;
private int age;
public Student() {
}
public Student(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Student{name=" + name + " , age=" +age + "}";
}
@Override
public boolean equals(Object obj) {
//1.判断两个对象是否为同一个引用
if(this== obj){
return true;
}
//2.判断obj是否为空
if (obj == null) {
return false;
}
//3.判断是否为同一个类型
// if(this.getClass()==obj.getClass()){
// return true;
// }
//instanceof 判断对象是否是某种类型
if (obj instanceof Student){
//4.强制类型转换
Student s=(Student)obj;
//5.比较属性
if (this.name.equals(s.getName())&&this.age==(s.getAge())){
return true;
}
}
return false;
}
}
package object;
public class TestStudent {
public static void main(String[] args) {
//equals方法:判断两个对象是否相等
Student student4 = new Student("小红",16);
Student student5 = new Student("小红",16);
System.out.println(student4.equals(student5));//equals方法重写后返回为true,为重写时比较的是地址
}
}
finalize()方法
- 当对象被判定为垃圾对象时,由JVM自动调节此方法,用以标记垃圾对象,进入回收队列
- 垃圾对象:没有有效引用指向此对象时,为垃圾对象
- 垃圾回收:由GC销毁垃圾对象,释放数据储存空间
- 自动回收机制:JVM的内存耗尽,一次性回收所有垃圾对象
- 手动回收机制:使用System.gc();通知JVM执行垃圾回收
package object;
import com.sun.org.apache.xpath.internal.objects.XObject;
public class Student {
private String name;
private int age;
@Override
protected void finalize() throws Throwable {
System.out.println(this.name+"对象被回收了");
}
}
package object;
public class TestStudent2 {
public static void main(String[] args) {
// Student s1 = new Student("aaa",20);
// Student s2 = new Student("bbb",20);
// Student s3 = new Student("ccc",20);
// Student s4 = new Student("ddd",20);
// Student s5 = new Student("eee",20);
new Student("aaa",20);
new Student("bbb",20);
new Student("ccc",20);
new Student("ddd",20);
new Student("eee",20);
//回收垃圾
System.gc();
System.out.println("回收垃圾完毕");
}
}
- 第一中方式不能回收垃圾,自己的理解是
第二种方式只在堆中分配了空间,并没有指向,被视为垃圾文件而回收