3月24日

package com.qiku.day19;

import java.util.*;

public class Zuo01 {
    public static void main(String[] args) {
        /**
         * 1、有如下map:
         * Map<String,String> map = new HashMap<>();
         * map.put(“aaa”,“111”);
         * map.put(“bbb”,“111”);
         * map.put(“ccc”,“111”);
         * map.put(“ddd”,“222”);
         * 使用3种方式，遍历并打印
         */
        Map<String,String> map = new HashMap<>();
        map.put("aaa","111");
        map.put("bbb","111");
        map.put("ccc","111");
        map.put("ddd","222");
        Collection<String> values = map.values();
        Iterator<String> valueIt = values.iterator();
        while (valueIt.hasNext()){
            String value = valueIt.next();
            System.out.println(value);
        }
        System.out.println("======================");
        Set<Map.Entry<String, String>> entries = map.entrySet();
        Iterator<Map.Entry<String, String>> entryIt = entries.iterator();
        while (entryIt.hasNext()){
            Map.Entry<String, String> entry = entryIt.next();
            String key = entry.getKey();
            String value = entry.getValue();
            System.out.println(key + "," + value);
        }
        System.out.println("=====================");
        Set<String> keys = map.keySet();
        Iterator<String> itKey = keys.iterator();
        while (itKey.hasNext()){
            String key = itKey.next();
            String value = map.get(key);
            System.out.println(key + "," + value);
        }
    }
}

package com.qiku.day19;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Zuo02 {
    public static void main(String[] args) {
        /**
         * 2、定义集合List， 依次将1，2，3，4，5，6，7，8，9 添加到集合中
         * 使用Collections中的方法：
         *   打乱顺序 求最大值 求最小值 升序排列 交换位置
         *   将该集合所有元素拷贝到另一个集合中并打印
         */
        List<Integer> list = new ArrayList<>();
        for (int i = 1; i < 10; i++) {
            list.add(i);
        }
        Collections.shuffle(list);
        System.out.println("打乱顺序:"+list);
        Integer max = Collections.max(list);
        System.out.println("最大值:"+max);
        Integer min = Collections.min(list);
        System.out.println("最小值:"+min);
        Collections.sort(list);
        System.out.println("升序排列:"+list);
        Collections.swap(list,3,4);
        System.out.println("交换位置:"+list);
        List<Integer> str = new ArrayList<>();
        for (int i = 0; i < 9; i++) {
            str.add(1);
        }
        Collections.copy(str,list);
        System.out.println("元素拷贝:"+str);

    }
}

package com.qiku.day19;

import java.util.Arrays;
import java.util.Scanner;

public class Zuo03 {
    public static void main(String[] args) {
        /**
         * 3、编写代码，模拟如下异常：
         */
        //ArithmeticException类 - 算术异常
        int a = 1;
        System.out.println(a / 0);
        //ArrayIndexOutOfBoundsException类 - 数组下标越界异常
        int[] arr = new int[2];
        arr[2] = 1;
        //NullPointerException - 空指针异常
        arr = null;
        System.out.println(arr.length);
        //ClassCastException - 类型转换异常
        A b = new B();
        C c = (C) b;
        System.out.println(c);
        //NumberFormatException - 数字格式异常
        int d = Integer.parseInt("abc");
        System.out.println(d);
        //OutOfMemoryError - 内存溢出错误
        String e = "a";
        for (int i = 0; i < 100000; i++) {
            e += e;
        }
        System.out.println(e);

    }
}

class A {
}

class B extends A {
}

class C extends B {
}

package com.qiku.day19;

import java.util.Arrays;

public class Zuo04 {
    public static void main(String[] args) {
        /**
         * 4、分析以下需求，并用代码实现：
         *     (1)统计每个单词出现的次数
         *     (2)有如下字符串
         *     "If you want to change your fate I think you must come to the school to learn java"(用空格间隔)
         *     (3)打印格式：
         *        to=3
         *        think=1
         *        you=2
         */
        String str="If you want to change your fate I think you must come to the school to learn java";
        String[] strs = str.split(" ");
        System.out.println(Arrays.toString(strs));
        for (int i = 0; i < strs.length; i++) {
            String a = strs[i];
            int b = 0;
            int c = str.indexOf(a);
            while (c!=-1){
                b++;
                c=str.indexOf(a,c+a.length());
            }
            System.out.println(a+"="+b);
        }
    }
}