【187天】黑马程序员27天视频学习笔记【Day15-中】-白红宇

【187天】黑马程序员27天视频学习笔记【Day15-中】

阅读量：6504 次

发布时间：2019-06-24

本文共 9662 字，大约阅读时间需要 32 分钟。

叨逼叨两句

开始干另外一件大事了，这个事搞定就好啦~好啦好啦~

15-3：Collection基本功能

方法

remove

contains

clear

isEmpty

size

package com.test.regex;import java.util.ArrayList;import java.util.Collection;@SuppressWarnings({"unchecked","rawtypes"})public class Demo18 {    public static void main(String[] args) {        Collection c = new ArrayList(); //父类引用指向子类对象        boolean b2 = c.add(true);        //自动装箱了   new Boolean(true)        boolean b3 = c.add(100);        //自动装箱了        boolean b4 = c.add(new Student("张三",23));        boolean b5 = c.add("abc");            //add方法如果是List集合，一直都会返回true，因为List可以存储重复的元素        //add方法如果是Set集合，则当存储重复元素时，会返回false                Collection c2 = new ArrayList();        boolean d1 = c2.add("a");        boolean d2 = c2.add("b");        boolean d3 = c2.add("c");        boolean d4 = c2.add("d");        System.out.println(c2);        c2.remove("b");        System.out.println(c2);        boolean s = c2.contains("a");        System.out.println(s);        c2.clear();        System.out.println(c2.isEmpty());        System.out.println(c2.size());        }}

15-4:集合的遍历之集合转数组遍历

package com.test.regex;import java.util.ArrayList;import java.util.Collection;public class Demo19 {    public static void main(String[] args) {        //demo1();                Collection c = new ArrayList();        c.add(new Student("张三",23));   //Object obj = new Student("张三",23);        c.add(new Student("张四",23));        c.add(new Student("张五",23));        c.add(new Student("张六",23));            Object[] arr = c.toArray();                for (int i = 0; i < arr.length; i++) {            //System.out.println(arr[i]);                Student s = (Student)arr[i];            System.out.println(s.getName());                    }            }    public static void demo1() {        Collection c = new ArrayList();        c.add("a");        c.add("b");        c.add("c");        c.add("d");                Object[] arr = c.toArray();        for (int i = 0; i < arr.length; i++) {            System.out.println(arr[i]);        }    }}

15-5：Collection集合的带All功能测试

addAll

package com.test.regex;import java.util.ArrayList;import java.util.Collection;public class Demo20 {    public static void main(String[] args) {        Collection c1 = new ArrayList();        c1.add("a");        c1.add("b");        c1.add("c");        c1.add("d");                Collection c2 = new ArrayList();        c2.add("a");        c2.add("b");        c2.add("c");        c2.add("d");                System.out.println(c1);        c1.addAll(c2);        System.out.println(c1);            }}

removeAll

package com.test.regex;import java.util.ArrayList;import java.util.Collection;public class Demo20 {    public static void main(String[] args) {        Collection c1 = new ArrayList();        c1.add("a");        c1.add("b");        c1.add("a");        c1.add("b");        c1.add("c");        c1.add("d");                Collection c2 = new ArrayList();        c2.add("a");        c2.add("b");                        System.out.println(c1);        c1.removeAll(c2);        System.out.println(c1);            }}

containsAll

package com.test.regex;import java.util.ArrayList;import java.util.Collection;public class Demo20 {    public static void main(String[] args) {        Collection c1 = new ArrayList();        c1.add("a");        c1.add("b");        c1.add("c");        c1.add("d");                Collection c2 = new ArrayList();        c2.add("a");        c2.add("b");                Collection c3 = new ArrayList();        c3.add("a");        c3.add("b");        c3.add("z");                System.out.println(c1);        boolean s1= c1.containsAll(c2);        boolean s2 = c1.containsAll(c3);        System.out.println(s1);        System.out.println(s2);            }}

retainAll

package com.test.regex;import java.util.ArrayList;import java.util.Collection;public class Demo20 {    public static void main(String[] args) {        Collection c1 = new ArrayList();        c1.add("a");        c1.add("b");        c1.add("c");        c1.add("d");                Collection c2 = new ArrayList();        c2.add("a");        c2.add("b");                Collection c3 = new ArrayList();        c3.add("a");        c3.add("b");        c3.add("c");        c3.add("d");        c3.add("e");        c3.add("f");                //取交集，若取完交集后，调用方法的c1的元素改变了，就返回true，若没有改变就返回false//        boolean s1= c1.retainAll(c2);//        System.out.println(s1);//        System.out.println(c1);                boolean s2 = c1.retainAll(c3);        System.out.println(s2);        System.out.println(c1);            }}

15-6:集合的遍历之迭代器

package com.test.regex;import java.util.ArrayList;import java.util.Collection;import java.util.Iterator;public class Demo21 {    public static void main(String[] args) {        Collection c1  = new ArrayList();        c1.add("a");        c1.add("b");        c1.add("c");        c1.add("d");                Iterator it1 = c1.iterator();        while(it1.hasNext()){            Object a = it1.next();            System.out.println(a);        }                Collection c2 = new ArrayList();        c2.add(new Student("张三",23));        c2.add(new Student("张四",24));        c2.add(new Student("张五",25));        c2.add(new Student("张六",26));                Iterator it2 = c2.iterator();        while(it2.hasNext()){            Student s = (Student)it2.next();            System.out.println(s.getName()+"   "+s.getAge());        }            }}

15-7:无

15-8:迭代器的原理及源码解析

迭代器原理

迭代器是对集合进行遍历,而每一个集合内部的存储结构都是不同的,所以每一个集合存和取都是不一样,那么就需要在每一个类中定义hasNext()和next()方法,这样做是可以的,但是会让整个集合体系过于臃肿,迭代器是将这样的方法向上抽取出接口,然后在每个类的内部,定义自己迭代方式,这样做的好处有二,第一规定了整个集合体系的遍历方式都是hasNext()和next()方法,第二,代码有底层内部实现,使用者不用管怎么实现的,会用即可

源码解析

public Iterator
    
      iterator() {        return new Itr();    }

private class Itr implements Iterator
    
      {        int cursor;       // index of next element to return        int lastRet = -1; // index of last element returned; -1 if no such        int expectedModCount = modCount;        public boolean hasNext() {            return cursor != size;        }        @SuppressWarnings("unchecked")        public E next() {            checkForComodification();            int i = cursor;            if (i >= size)                throw new NoSuchElementException();            Object[] elementData = ArrayList.this.elementData;            if (i >= elementData.length)                throw new ConcurrentModificationException();            cursor = i + 1;            return (E) elementData[lastRet = i];        }        public void remove() {            if (lastRet < 0)                throw new IllegalStateException();            checkForComodification();            try {                ArrayList.this.remove(lastRet);                cursor = lastRet;                lastRet = -1;                expectedModCount = modCount;            } catch (IndexOutOfBoundsException ex) {                throw new ConcurrentModificationException();            }        }

15-9：List集合特有功能概述和测试

package com.test.regex;import java.util.ArrayList;import java.util.List;public class Demo22 {    public static void main(String[] args) {        List list = new ArrayList();//开发一般是直接ArrayList list = new ArrayList();        list.add("a");        list.add("b");        list.add("c");        list.add("d");        //list.add(1,"e");        //list.add(10,"f");        //list.add(4,"f");     //index <= size 都可以        System.out.println(list);    }}

remove

package com.test.regex;import java.util.ArrayList;import java.util.List;public class Demo22 {    public static void main(String[] args) {        List list = new ArrayList();//开发一般是直接ArrayList list = new ArrayList();        list.add("a");        list.add("b");        list.add("c");        list.add("d");                Object obj = list.remove(1);        System.out.println(obj); //移除的元素        System.out.println(list);  //剩下的集合元素    }}

package com.test.regex;import java.util.ArrayList;import java.util.List;public class Demo22 {    public static void main(String[] args) {        List list = new ArrayList();//开发一般是直接ArrayList list = new ArrayList();        list.add(111);        list.add(222);        list.add(333);                list.remove(111); //    删除时不会自动装箱，111被当成了索引        System.out.println(list);                    }}

package com.test.regex;import java.util.ArrayList;import java.util.List;public class Demo22 {    public static void main(String[] args) {        List list = new ArrayList();//开发一般是直接ArrayList list = new ArrayList();        list.add("a");        list.add("b");        list.add("c");                //list因为有索引，可以通过get方法来遍历        for (int i = 0; i < list.size(); i++) {            System.out.println(list.get(i));        }    }}

package com.test.regex;import java.util.ArrayList;import java.util.List;public class Demo22 {    public static void main(String[] args) {        List list = new ArrayList();//开发一般是直接ArrayList list = new ArrayList();        list.add("a");        list.add("b");        list.add("c");                list.set(1, "z");        System.out.println(list);    }}

15-10:List集合存储学生对象并遍历

package com.test.regex;import java.util.ArrayList;import java.util.List;public class Demo22 {    public static void main(String[] args) {        List list = new ArrayList();        list.add(new Student("张1",23));        list.add(new Student("张2",23));        list.add(new Student("张3",23));        list.add(new Student("张4",23));        list.add(new Student("张5",23));        for (int i = 0; i < list.size(); i++) {            //System.out.println(list.get(i));            Student temp = (Student)list.get(i);            System.out.println(temp.getName()+"   "+temp.getAge());        }    }}

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