【187天】黑马程序员27天视频学习笔记【Day15-中】

时间 2019-12-06

原文原文链接

叨逼叨两句

开始干另一件大事了，这个事搞定就好啦~好啦好啦~java

15-3：Collection基本功能

方法

add
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方法若是是List集合，一直都会返回true，由于List能够存储重复的元素
        //add方法若是是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,而每个集合内部的存储结构都是不一样的,因此每个集合存和取都是不同,那么就须要在每个类中定义hasNext()和next()方法,这样作是能够的,可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,而后在每一个类的内部,定义本身迭代方式,这样作的好处有二,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,会用便可数组

源码解析

public Iterator<E> iterator() {
        return new Itr();
    }

private class Itr implements Iterator<E> {
        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();//开发通常是直接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 均可以
        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();//开发通常是直接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();//开发通常是直接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();//开发通常是直接ArrayList list = new ArrayList();
        list.add("a");
        list.add("b");
        list.add("c");
        
        //list由于有索引，能够经过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();//开发通常是直接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());
        }
    }
}