怎么就没程序入口了 main函数里面怎么调用前面的属性方法我还不知道呢？？

package chapter2;

public class Telephone02 {

private float screen;

private float cpu;

private float mem;

public float getScreen() {

return screen;

}

public void setScreen(float screen) {

this.screen = screen;

}

public float getCpu() {

return cpu;

}

public void setCpu(float cpu) {

this.cpu = cpu;

}

public float getMem() {

return mem;

}

public void setMem(float mem) {

this.mem = mem;

}

public Telephone02() {

 System.out.println("无参的构造方法执行了!");

}

 public Telephone02(float newscreen,float newcpu,float newmem) {

 screen=newscreen;

 cpu = newcpu;

 mem = newmem;

 System.out.println("有参的构造方法执行了!");

 }

}