Java类型转换

Java支持的类型转换：

1.类型转换原生数据类型

隐式转换：

数据类型自动转换为另一种数据类型，发生前提是两种数据类型彼此兼容

较小数据类型放入较大数据类型

int a=100;
long b=a;

显式转换：

必须是转换为兼容类型

较大数据类型放入较小数据类型

longa=100;
int b=(int)a;

2.对象的类型转换

向上转型

向下转型

向上转型：子类引用赋值给父类引用

Employee e1=new Employee();
Manager mgr=new Manager();
e1=mgr;

向下转型：子类实例化父类

public class Employee {

	private int id;
	private String name;
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String toString() {
		return "Employee [id=" + id + ", name=" + name + "]";
	}
	
}
public class Manager extends Employee {

	
	private int bonus;

	public int getBonus() {
		return bonus;
	}

	public void setBonus(int bonus) {
		this.bonus = bonus;
	}

	public String toString() {
		return "Manager [bonus=" + bonus + ", toString()=" + super.toString()
				+ "]";
	}
	

}

public class Test {
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Employee e1=new Manager();//向下转型
		e1.setId(12);
		e1.setName("xiaoming");
		//虽然使用Manager实例化的e1,但是e1却没有Manager的bonus属性，必须强转为Manager
		Manager magr=(Manager) e1;
		magr.setBonus(10000);
		System.out.println(e1);
		System.out.println(magr);
		//e1和magr的内容相同，因为是同一个引用
		/*
		 * Manager [bonus=10000, toString()=Employee [id=12, name=xiaoming]]
		 * Manager [bonus=10000, toString()=Employee [id=12, name=xiaoming]]
		 */
		Employee e2=magr;//向上 转型
		e2.setId(2);//e1没有Manager的bonus属性
		System.out.println(e2);
		System.out.println(e1);
		System.out.println(magr);
		/*
		 * Manager [bonus=10000, toString()=Employee [id=2, name=xiaoming]]
		 * Manager [bonus=10000, toString()=Employee [id=2, name=xiaoming]]
         * Manager [bonus=10000, toString()=Employee [id=2, name=xiaoming]]
		 */
		//同一个引用
	}

}

在其位谋其职，要想弄明白是否能调用setBonus()就要看他的声明类型，而不是看他转换为了什么类型，这个要明白

        Employee e=new Employee();
		e.setId(23);
		e.setName("lili");
		Manager m1=new Manager();
		m1=(Manager)e;//Code.Employee cannot be cast to Code.Manager
						//报错了，弄明白再转

Employee e=new Employee();
		e.setId(23);
		e.setName("lili");
		Manager m1=new Manager();
		//m1=(Manager)e;//Code.Employee cannot be cast to Code.Manager
						//报错了，弄明白再转
		m1.setId(12);
		m1.setName("wangwu");
		m1.setBonus(12233);
		System.out.println(m1);
		System.out.println(e);
		/*
		 * Manager [bonus=12233, toString()=Employee [id=12, name=wangwu]]
		 * Employee [id=23, name=lili]
		 */