3.24作业

package com.qiku.day18;

import java.util.*;

public class Zy1 {
    public static void main(String[] args) {
        Map<String,String> map = new HashMap<>();
        map.put("aaa","111");
        map.put("bbb","111");
        map.put("ccc","111");
        map.put("ddd","222");
        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);
        }
        Collection<String> values = map.values();
        Iterator<String> valueIt = values.iterator();
        while (valueIt.hasNext()){
            String value = valueIt.next();
            System.out.println(value);
        }
        Set<Map.Entry<String,String>> entries = map.entrySet();
        Iterator<Map.Entry<String,String>> iterator = entries.iterator();
        System.out.println("[");
        while (iterator.hasNext());
        System.out.println(iterator.next());
        if (iterator.hasNext()){
            System.out.println(",");
        }else  {
            System.out.println("]");
        }
    }
}

package com.qiku.day18;

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

public class Zy2 {
    //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
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>();
        for (int i = 1; i < 10; i++) {
            list.add(i);
        }
        Collections.shuffle(list);
        System.out.println("打乱：" + list);
        Integer max = Collections.max(list);
        System.out.println("max:" + max);
        Integer min = Collections.min(list);
        System.out.println("min:" + min);
        Collections.sort(list);
        System.out.println("升序：" + list);
        Collections.swap(list,2,5);
        System.out.println("交换：" + list);
        List<Integer> list1 = new ArrayList<>();
        for (int i = 0; i < list.size(); i++) {
            list1.add(1);
        }
        Collections.copy(list1,list);
        System.out.println(list1);
    }
}

package com.qiku.day18;

public class Zy3 {
    //3、编写代码，模拟如下异常：
    // ArithmeticException类 - 算术异常
    // ArrayIndexOutOfBoundsException类 - 数组下标越界异常
    // NullPointerException - 空指针异常
    // ClassCastException - 类型转换异常
    // NumberFormatException - 数字格式异常
    // OutOfMemoryError - 内存溢出错误
    public static void main(String[] args) {
        //ArithmeticException - 算术异常
//        System.out.println(7/0);
        //ArrayIndexOutOfBoundsException - 数组下标越界异常
        int[] arr = new int[5];
//        System.out.println(arr[8]);
        //NullPointerException - 空指针异常
        arr = null;
//        arr[0] = 3;
        //ClassCastException - 类型转换异常
//        A a = new B();
//        C c = (C) a;
        //NumberFormatException - 数字格式异常
//        int x = Integer.parseInt("aaa");
        //OutOfMemoryError - 内存溢出错误
        String str = "aaa";
//        for (int i = 0; i < 10000; i++) {
//            str += str;
//        }
    }
}

class A {
}

class B extends A {
}

class C extends A {
}

package com.qiku.day18;

import java.util.*;

public class Zy4 {
    //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
    public static void main(String[] args) {
        String str = "If you want to change your fate I think you must come to the school to learn java";
        String[] s= str.split(" ");
        System.out.println(Arrays.toString(s));
        Map<String,Integer> map = new HashMap<>();
        for (int i = 0; i < s.length; i++) {
            if (map.get(s[i]) == null){
                map.put(s[i] , 1);
            }else {
                int value = map.get(s[i]);
                map.put(s[i],value+1);
            }
        }
        System.out.println(map);
        Set<String> keys = map.keySet();
        Iterator<String> it = keys.iterator();
        while (it.hasNext()){
            String key = it.next();
            Integer value = map.get(key);
            System.out.println(key + "=" + value);
        }
    }
}