this为一系统资源,只允许用户读而不允许写,它存放当前对象的地址(引用)。
this变量有以下作用:
1. 构造方法重用:
public class Rectangle{
public Rectangle(Location at, Shape size) {…}
public Rectangle(Shape size,Location at){
this(at, size); }
public Rectangle(Location at) {
this(at, new Shape(100,100));
}
public Rectangle(Shape size) {
this(size, new Location(1,1));
}
public Rectangle() {
this(new Location(1,1), new Shape(100,100));
}
}
2、消除歧义:
Location{
private int x;
private int y;
public Location(int x,int y) {
this.x=x;
this.y=y;
}
……
}
3、返回对象-链式方法调用:
public class Count {
private int i = 0;
Count increment() {
i++;
return this; //返回对象的地址,所以我们可以链式访问它
}
void print() {
System.out.println("i = " + i);
}
}
public class CountTest{
public static void main(String[] args) {
Count x = new Count();
x.increment().increment().print();
}
}
4、作为参数传递"this”变量-进行回调:
假设有一个容器类和一个部件类,在容器类的某个方法中要创建部件类的实例对象,而部件类的构造方法要接受一个代表其所在容器的参数。例如:
class Container
{
Component comp;
public void addComponent()
{
comp = new Component(this); //代表你所创建的对象,因为它要用到.
}
}
class Component
{
Container myContainer;
public Component(Container c)
{
myContainer = c;
}
} |