2016/5/30学习记录

1.模拟栈

package Exercise;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Scanner;

public class Test {

    public static void main(String[] args) {
    ArrayList<Object> list = new ArrayList<>();
    Test a = new Test(list);
    System.out.print("is the steak empty? ");
    System.out.println(a.isEmpty());
    a.push(2);
    a.push(3);
    a.push(5);
    System.out.print("the size of the steak is ");
    System.out.println(a.getSize());
    System.out.print("is the steak empty? ");
    System.out.println(a.isEmpty());
    System.out.print("get the peek number ");
    System.out.println(a.peek());
    System.out.print("pop the peek and return it ");
    System.out.println(a.pop());
    System.out.print("now the peak is ");
    System.out.println(a.peek());
    System.out.print("the size of the steak ");
    System.out.println(a.getSize());
    System.out.print("list the numbers ");
    System.out.println(a.toString());
    }
    Test(ArrayList<Object> list){
        this.list = list;
    }
    //类Test模拟栈

    private ArrayList<Object> list;
    public boolean isEmpty(){
        return list.isEmpty();
    }
    public int getSize(){
        return list.size();
    }
    public Object peek(){
        return list.get(list.size()-1);
    }
    public Object pop(){
        Object o = list.get(list.size()-1);
        list.remove(list.size()-1);
        return o;
    }
    public void push(Object i){
        list.add(i);
    }
    public String toString(){
        return "the steak is "+ list.toString();
    }
}

输出如下

is the steak empty? true
the size of the steak is 3
is the steak empty? false
get the peek number 5
pop the peek and return it 5
now the peak is 3
the size of the steak 2
list the numbers the steak is [2, 3]

2.对象作为成员变量的例子，时钟。

package Exercise;

public class Times {
    private int limit;
    private int num = 0;

    Times(int limit) {
        this.limit = limit;
    }

    int getLimit() {
        return limit;
    }

    int getNum() {
        return num;
    }

    void tick() {
        num++;
        if (num == limit)
            num = 0;
    }

    void show() {
        while (true) {
            tick();
            System.out.println(num);
        }
    }

    public String toString() {
        if (num < 10)
            return "0" + num;
        else
            return "" + num;
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Times t = new Times(24);
        t.show();
    }

}

此函数定义了数字如何跳动。接下来在另一个类中引用两个Times的对象作为变量

 1 package Exercise;
 2
 3 public class ShowTime {
 4     private Times hours = new Times(24);
 5     private Times minutes = new Times(60);
 6
 7     void show() {
 8         while (true) {
 9             minutes.tick();
10             if (minutes.getNum() == 0)
11                 hours.tick();
12             // System.out.printf("%02d:%02d\n",hours.getNum()
13             // ,minutes.getNum());
14             System.out.println(hours + ":" + minutes);
15         }
16
17     }
18
19     public static void main(String[] args) {
20         // TODO Auto-generated method stub
21         ShowTime st = new ShowTime();
22         st.show();
23         // String s = "123";
24         // Integer i = 12;
25         // s=i+"";
26         // System.out.println(s);
27     }
28
29 }

其中第14行，直接用hours和minutes调用了Times中的toString函数，因为hours+":"编译器判断时会默认hours为字符串，所以直接调用之。