Java中Object类的理解和使用

method(Object obj){…} //可以接收任何类作为其参数
Person o = new Person();  
method(o);

public class Person {
	...
}
//上面和下面是等价的
public class Person extends Object {
	...
}

class User{
	private String host;
	private String username;
	private String password;
	public User(String host, String username, String password) {
		super();
		this.host = host;
		this.username = username;
		this.password = password;
	}
	public User() {
		super();
	}
	public String getHost() {
		return host;
	}
	public void setHost(String host) {
		this.host = host;
	}
	public String getUsername() {
		return username;
	}
	public void setUsername(String username) {
		this.username = username;
	}
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}
	@Override
	public String toString() {
		return "User [host=" + host + ", username=" + username + ", password=" + password + "]";
	}
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		User other = (User) obj;
		if (host == null) {
			if (other.host != null)
				return false;
		} else if (!host.equals(other.host))
			return false;
		if (password == null) {
			if (other.password != null)
				return false;
		} else if (!password.equals(other.password))
			return false;
		if (username == null) {
			if (other.username != null)
				return false;
		} else if (!username.equals(other.username))
			return false;
		return true;
	}
}

Date now=new Date();
System.out.println("now="+now); //相当于"now="+now.toString()

public static void main(String[] args) {
	Object obj = new Person();
	System.out.println(obj.getClass()); //获取运行时类型
}

public static void main(String[] args) {
	System.out.println("Aa".hashCode()); //2112
	System.out.println("BB".hashCode()); //2112
}

public class CloneTest {
	public static void main(String[] args) {
		Animal a1 = new Animal("小黑");
		try {
			Animal a2 = (Animal) a1.clone();
			System.out.println("原始对象：" + a1);
			a2.setName("小黄");
			System.out.println("clone的对象：" + a2);
		} catch (CloneNotSupportedException e) {
			e.printStackTrace();
		}
	}
}
class Animal implements Cloneable{
	private String name;
	public Animal() {
		super();
	}
	public Animal(String name) {
		super();
		this.name = name;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	@Override
	public String toString() {
		return "Animal [name=" + name + "]";
	}
	@Override
	protected Object clone() throws CloneNotSupportedException {
		return super.clone();
	}
}

public class FinalizeTest {
	public static void main(String[] args) {
		Person p = new Person("Peter", 12);
		System.out.println(p);
		p = null; //此时对象实体就是垃圾对象，等待被回收,但时间不确定
		System.gc();//强制性释放空间
	}
}
class Person{
	private String name;
	private int age;
	public Person(String name, int age) {
		super();
		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;
	}
	//子类重写此方法，可在释放对象前进行某些操作
	@Override
	protected void finalize() throws Throwable {
		System.out.println("对象被释放--->" + this);
	}
	@Override
	public String toString() {
		return "Person [name=" + name + ", age=" + age + "]";
	}
}