2021-1-28
1. Comparison of collections and arrays
2. Collection architecture
Red represents the implementation class, blue represents the interface
3. Collection collection (overview, common methods)
package com.wc.collection;
import java.util.ArrayList;
import java.util.Collection;
/**
* @author wc
* @Date: 2021/01/29/9:29
*/
public class MyCollection {
public static void main(String[] args) {
//多态的方式
Collection<String> collection = new ArrayList<>();
//增加元素 add
collection.add("aaa");
collection.add("bbb");
collection.add("ccc");
collection.add("ddd");
//System.out.println(collection);
//methodRemove(collection);
//methodRemoveIf(collection);
//methodClear(collection);
//methodContain(collection);
//methodEmpty(collection);
//集合长度
int size = collection.size();
System.out.println(size);
}
private static void methodEmpty(Collection<String> collection) {
//判断是否为空
boolean empty = collection.isEmpty();
System.out.println(empty);
}
private static void methodContain(Collection<String> collection) {
//判断是否存在指定元素
boolean result = collection.contains("fff");
boolean result1 = collection.contains("aaa");
System.out.println(result);
System.out.println(result1);
}
private static void methodClear(Collection<String> collection) {
//清空集合
collection.clear();
System.out.println(collection);
}
private static void methodRemoveIf(Collection<String> collection) {
//根据条件进行删除,删除长度为3的元素
/*removeIf底层会遍历集合，得到集合没一个元素
* s表示集合中的每一个元素
* 就会把每个元素都到lambda表达式中去判断
* 如果是true，则删除
* false则保留*/
collection.removeIf(
(String s) -> {
return s.length() == 3;
}
);
System.out.println(collection);
}
private static void methodRemove(Collection<String> collection) {
//remove移除元素
boolean result = collection.remove("aaa");
boolean result1 = collection.remove("fff");
System.out.println(result);
System.out.println(result1);
}
}
4. Collection traversal (iterator)
package com.wc.collection;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
/**
* @author wc
* @Date: 2021/01/29/9:29
*/
public class MyCollection1 {
public static void main(String[] args) {
//多态的方式
Collection<String> collection = new ArrayList<>();
//增加元素 add
collection.add("aaa");
collection.add("bbb");
collection.add("ccc");
collection.add("ddd");
//创建迭代器
//一旦创建，默认指向元素0索引位置
Iterator<String> iterator = collection.iterator();
// //判断里面有没有元素可以取出
// System.out.println(iterator.hasNext());
// //取出当前元素，并指向下一个元素的索引
// System.out.println(iterator.next());
while (iterator.hasNext()){
System.out.println(iterator.next());
}
}
}
Case study
package com.wc.collection;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
/**
* @author wc
* @Date: 2021/01/29/9:29
*/
public class MyCollection2 {
public static void main(String[] args) {
//多态的方式
ArrayList<String> list = new ArrayList<>();
//增加元素 add
list.add("a");
list.add("b");
list.add("b");
list.add("c");
list.add("d");
//创建迭代器
//一旦创建，默认指向元素0索引位置
Iterator<String> iterator = list.iterator();
// //判断里面有没有元素可以取出
// System.out.println(iterator.hasNext());
// //取出当前元素，并指向下一个元素的索引
// System.out.println(iterator.next());
while (iterator.hasNext()){
String s=iterator.next();
if ("b".equals(s)){
iterator.remove();
}
}
System.out.println(list);
}
}
5. Enhance the for loop
package com.wc.collection;
import java.util.ArrayList;
import java.util.Iterator;
/**
* @author wc
* @Date: 2021/01/29/9:29
*/
public class MyCollection3 {
public static void main(String[] args) {
ArrayList<String> list = new ArrayList<>();
//增加元素 add
list.add("a");
list.add("b");
list.add("b");
list.add("c");
list.add("d");
//增强for循环
//1.数据类型一定是集合或者数组的元素类型
//2.s仅仅是一个变量而已，在循环过程中，依次表示集合或者数组中的每一个元素
//3.list就是被遍历的集合或者数组
for (String s : list) {
System.out.println(s);
}
}
}
6. List collection (overview, characteristics, unique methods)
7. Stacks and queues (understand)
Stack
queue
8. Arrays and linked lists (understand)
Array
linked list
9. LinkedList collection (special function) (understand)
10. Set collection (can be compared to List collection learning)
11.TreeSet collection (understand)
12. Use TreeSet natural sorting Comparable (compare to usage)
The case
sorts the age naturally through the interface Comparable
package com.wc.collection;
import java.util.TreeSet;
/**
* @author wc
* @Date: 2021/01/29/17:48
*/
public class TreeSetDemo {
public static void main(String[] args) {
TreeSet<Student> ts=new TreeSet<>();
Student student=new Student("zhangsan",18);
Student student1=new Student("lisi",20);
Student student2=new Student("wangwu",19);
Student student3=new Student("zhaoliu",18);
ts.add(student);
ts.add(student1);
ts.add(student2);
ts.add(student3);
System.out.println(ts);
}
}
13. Comparator sorting Comparator
package com.wc.collection;
import java.util.Comparator;
import java.util.TreeSet;
/**
* @author wc
* @Date: 2021/01/29/17:48
*/
public class TreeSetDemo {
public static void main(String[] args) {
TreeSet<Student> ts=new TreeSet<>(new Comparator<Student>() {
@Override
public int compare(Student o1, Student o2) {
//o1新传入的对象
//o2已经放入集合的对象
int result = o1.getAge() - o2.getAge();
result=result==0?o1.getName().compareTo(o2.getName()):result;
return result;
}
});
Student student=new Student("zhangsan",18);
Student student1=new Student("lisi",20);
Student student2=new Student("wangwu",19);
Student student3=new Student("zhaoliu",18);
ts.add(student);
ts.add(student1);
ts.add(student2);
ts.add(student3);
System.out.println(ts);
}
}
Summary of the two comparisons
