java-collection
1、Iterator
1.1 代码
package com.nash.java.core.ch01_collection;
import java.util.ArrayList;
import java.util.Iterator;
/**
* 1、迭代器 Iterator
* 迭代器是用来遍历集合元素的,通过迭代器,可以将遍历与数据分离
* while(it.hasNext()){
* System.out.println(it.next());
* }
*
* 2、Foreach
* 实现了Iterable接口,即可用Foreach遍历
* for(String s:set){
* System.out.println(s);
* }
*/
public class IteratorApp {
public static void main(String[] args) {
ArrayList<String> list = new ArrayList<String>();
list.add("a");
list.add("b");
list.add("c");
list.add("d");
// 1、iterator() 遍历,实现了iterator接口
System.out.print("Iterator 遍历:\t");
Iterator it = list.iterator();
while (it.hasNext()) {
System.out.print(it.next() + " ");
}
System.out.println();
// 2、foreach 遍历
System.out.print("Foreach 遍历:\t");
for (String li : list){
System.out.print(li + " ");
}
}
}
1.2 结果
Iterator 遍历: a b c d
Foreach 遍历: a b c d
2、ArrayList
2.1 代码
package com.nash.java.core.ch01_collection;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
/**
* 数组列表 ArrayList
* 有序、可重复集合。
*
* 容量可以动态增加,底层实现是数组
* 1、有序
* 2、元素个数不限
* 3、元素类型相同、定型
* 4、可变值
* 5、可重复
* 6、查找快、更新慢
*/
public class ArrayListApp {
public static void main(String[] args) {
// 初始化、集体赋值
List<String> list = Arrays.asList("hadoop","hbase","hive");
ArrayList<String> arrayList = new ArrayList<>(list);
System.out.println("arrayList:\t" + arrayList.toString());
System.out.println("equals():\t" + list.equals(arrayList));
// size() 列表长度
System.out.println("size():\t" + arrayList.size());
// isEmpty() 是否为空
System.out.println("isEmpty():\t" + arrayList.isEmpty());
// contains() 是否包含
System.out.println("contains(\"Flink\"):\t" + arrayList.contains("hadoop"));
// 初始化、逐个赋值
ArrayList<String> courseList=new ArrayList<>();
System.out.println("courseList:\t" + courseList);
// add() 插入
courseList.add("Java");
System.out.println("add(\"Java\"):\t" + courseList);
courseList.add("Python");
System.out.println("add(\"Python\"):\t" + courseList);
courseList.add("Scala");
System.out.println("add(\"Scala\"):\t" + courseList);
courseList.add(0,"First");
System.out.println("add(0,\"First\"):\t" + courseList);
// set() 更新
courseList.set(0,"Go");
System.out.println("set(0,\"Go\"):\t" + courseList);
// get() 查询
System.out.println("get(3):\t" + courseList.get(2));
// remove() 删除
courseList.remove(0);
System.out.println("remove(0):\t" + courseList);
courseList.remove("Scala");
System.out.println("remove(\"Scala\"):\t" + courseList);
// fori 遍历
System.out.print("fori():\t");
for (int i = 0; i < courseList.size(); i++) {
System.out.print(courseList.get(i) + " ");
}
System.out.println();
// foreach 遍历,实现了iterable接口
System.out.print("foreach():\t");
for (String course:courseList){
System.out.print(course + " ");
}
System.out.println();
// iterator() 遍历,实现了iterator接口
System.out.print("iterator():\t");
Iterator<String> courseIterator = courseList.iterator();
while (courseIterator.hasNext()){
System.out.print(courseIterator.next() + " ");
}
System.out.println();
// subList(1,2) 子表
System.out.println("subList(1,2):\t" + courseList.subList(1,2));
}
}
2.2 结果
arrayList: [hadoop, hbase, hive]
equals(): true
size(): 3
isEmpty(): false
contains("Flink"): true
courseList: []
add("Java"): [Java]
add("Python"): [Java, Python]
add("Scala"): [Java, Python, Scala]
add(0,"First"): [First, Java, Python, Scala]
set(0,"Go"): [Go, Java, Python, Scala]
get(3): Python
remove(0): [Java, Python, Scala]
remove("Scala"): [Java, Python]
fori(): Java Python
foreach(): Java Python
iterator(): Java Python
subList(1,2): [Python]
3、LinkedList
3.1 代码
package com.nash.java.core.ch01_collection;
import java.util.*;
/**
* 链表 LinkedList
* 有序、可重复集合。
*
* 底层实现是指针、内部类
* 1、有序
* 2、元素个数不限
* 3、元素类型相同、定型
* 4、可变值
* 5、可重复
* 6、查找慢、插入/删除/更新快
*/
public class LinkedListApp {
public static void main(String[] args) {
// 初始化、集体赋值
List<String> list = Arrays.asList("Java","Python","Scala");
LinkedList<String> linkedList = new LinkedList<>(list);
System.out.println("linkedList:\t" + linkedList.toString());
System.out.println("equals():\t" + list.equals(linkedList));
// size() 列表长度
System.out.println("size():\t" + linkedList.size());
// isEmpty() 是否为空
System.out.println("isEmpty():\t" + linkedList.isEmpty());
// contains() 是否包含
System.out.println("contains(\"Java\"):\t" + linkedList.contains("Java"));
// 初始化、逐个赋值
LinkedList<String> courseList=new LinkedList<>();
System.out.println("courseList:\t" + courseList);
// add() 插入
courseList.add("Hadoop");
System.out.println("add(\"Hadoop\"):\t" + courseList);
courseList.add("HBase");
System.out.println("add(\"HBase\"):\t" + courseList);
courseList.add("Hive");
System.out.println("add(\"Hive\"):\t" + courseList);
// add(0,"First")
courseList.add(0,"First");
System.out.println("add(0,\"First\"):\t" + courseList);
// addFirst("Spark")
courseList.addFirst("Spark");
System.out.println("addFirst(\"Spark\"):\t" + courseList);
// addLast("Flink")
courseList.addLast("Flink");
System.out.println("addLast(\"Flink\"):\t" + courseList);
// set() 更新
courseList.set(0,"Hama");
System.out.println("set(0,\"Hama\"):\t" + courseList);
// get() 查询
System.out.println("get(3):\t" + courseList.get(3));
// remove() 删除
courseList.remove(0);
System.out.println("remove(0):\t" + courseList);
courseList.remove("First");
System.out.println("remove(\"First\"):\t" + courseList);
/**
* poll()
* 1、数据结构:队列(Queue)
* 2、方法:出队(Dequeue)
* 3、方法说明:查看队首元素,并删除该元素
* 4、类比:remove() 删除
*/
System.out.println("poll():\t" + courseList.poll());
System.out.println("courseList:\t" + courseList);
/**
* offer()
* 1、数据结构:队列(Queue)
* 2、方法:入队(Deque)
* 3、方法说明:在队尾插入元素
* 4、类比:add() 插入
*/
System.out.println("offer():\t" + courseList.offer("Hama"));
System.out.println("courseList:\t" + courseList);
/**
* peek()
* 1、数据结构:队列(Queue)
* 2、方法:查队
* 3、方法说明:查看队首元素,不删除
* 4、类比:getFirst()
*/
System.out.println("peek():\t" + courseList.peek());
System.out.println("courseList:\t" + courseList);
// element()、getFirst() 查看首元素
System.out.println("element():\t" + courseList.element());
/**
* pop()
* 1、数据结构:堆栈(Stack)
* 2、方法:出栈
* 3、方法说明:移除堆栈顶部元素
* 4、类比:remove() 删除
*/
System.out.println("pop():\t" + courseList.pop());
System.out.println("courseList:\t" + courseList);
/**
* push()
* 1、数据结构:堆栈(Stack)
* 2、方法:入栈(Dequeue)
* 3、方法说明:把元素压入堆栈顶部
* 4、类比:addFirst() 在顶部插入元素
*/
courseList.push("Samza");
System.out.println("push():\t" + courseList);
// fori 遍历
System.out.print("fori():\t");
for (int i = 0; i < courseList.size(); i++) {
System.out.print(courseList.get(i) + " ");
}
System.out.println();
// foreach 遍历,实现了iterable接口
System.out.print("foreach():\t");
for (String course:courseList){
System.out.print(course + " ");
}
System.out.println();
// iterator() 遍历,实现了iterator接口
System.out.print("iterator():\t");
Iterator<String> courseIterator = courseList.iterator();
while (courseIterator.hasNext()){
System.out.print(courseIterator.next() + " ");
}
System.out.println();
// subList(1,2) 子表
System.out.println("subList(1,2):\t" + courseList.subList(1,2));
}
}
3.2 结果
linkedList: [Java, Python, Scala]
equals(): true
size(): 3
isEmpty(): false
contains("Java"): true
courseList: []
add("Hadoop"): [Hadoop]
add("HBase"): [Hadoop, HBase]
add("Hive"): [Hadoop, HBase, Hive]
add(0,"First"): [First, Hadoop, HBase, Hive]
addFirst("Spark"): [Spark, First, Hadoop, HBase, Hive]
addLast("Flink"): [Spark, First, Hadoop, HBase, Hive, Flink]
set(0,"Hama"): [Hama, First, Hadoop, HBase, Hive, Flink]
get(3): HBase
remove(0): [First, Hadoop, HBase, Hive, Flink]
remove("First"): [Hadoop, HBase, Hive, Flink]
poll(): Hadoop
courseList: [HBase, Hive, Flink]
offer(): true
courseList: [HBase, Hive, Flink, Hama]
peek(): HBase
courseList: [HBase, Hive, Flink, Hama]
element(): HBase
pop(): HBase
courseList: [Hive, Flink, Hama]
push(): [Samza, Hive, Flink, Hama]
fori(): Samza Hive Flink Hama
foreach(): Samza Hive Flink Hama
iterator(): Samza Hive Flink Hama
subList(1,2): [Hive]
4、HashSet
4.1 代码
package com.nash.java.core.ch01_collection;
import java.util.HashSet;
import java.util.Iterator;
/**
* 集合实现类 HashSet
* 无序、不可重复集合。
*
* 通过散列机制将信息存储到哈希表
* 当程序向HashSet集合添加元素时,HashSet会根据该元素的HashCode值,计算它在内存的存储位置,这样可以快速定位该元素。
* 1、无序
* 2、元素个数不限
* 3、元素类型相同、定型
* 4、可变值
* 5、不可重复
* 6、查找慢、插入/删除/更新快
*/
public class HashSetApp {
public static void main(String[] args) {
// 初始化、逐个赋值
HashSet<String> courseSet=new HashSet<>();
System.out.println("courseSet:\t" + courseSet);
// size() 列表长度
System.out.println("size():\t" + courseSet.size());
// isEmpty() 是否为空
System.out.println("isEmpty():\t" + courseSet.isEmpty());
// contains() 是否包含
System.out.println("contains(\"Java\"):\t" + courseSet.contains("Java"));
// add() 插入
courseSet.add("Java");
System.out.println("add(\"Java\"):\t" + courseSet);
courseSet.add("Python");
System.out.println("add(\"Python\"):\t" + courseSet);
courseSet.add("Scala");
System.out.println("add(\"Scala\"):\t" + courseSet);
courseSet.add("Scala");
System.out.println("add(\"Scala\"):\t" + courseSet);
// remove() 删除
courseSet.remove("Scala");
System.out.println("remove(\"Scala\"):\t" + courseSet);
// foreach 遍历,实现了iterable接口
System.out.print("foreach():\t");
for (String course:courseSet){
System.out.print(course + " ");
}
System.out.println();
// iterator() 遍历,实现了iterator接口
System.out.print("iterator():\t");
Iterator<String> courseIterator = courseSet.iterator();
while (courseIterator.hasNext()){
System.out.print(courseIterator.next() + " ");
}
System.out.println();
}
}
4.2 结果
courseSet: []
size(): 0
isEmpty(): true
contains("Java"): false
add("Java"): [Java]
add("Python"): [Java, Python]
add("Scala"): [Java, Scala, Python]
add("Scala"): [Java, Scala, Python]
remove("Scala"): [Java, Python]
foreach(): Java Python
iterator(): Java Python
5、TreeSet
5.1 代码
package com.nash.java.core.ch01_collection;
import java.util.Iterator;
import java.util.TreeSet;
/**
* 集合实现类 TreeSet
* 有序、不可重复集合。
*
* 采用红黑树的数据结构存储集合元素。
*
* 当程序向TreeSet集合添加元素时,TreeSet会根据该元素的HashCode值,计算它在内存的存储位置,这样可以快速定位该元素。
* 1、有序
* 2、元素个数不限
* 3、元素类型相同、定型
* 4、可变值
* 5、不可重复
* 6、查找慢、插入/删除/更新快
*/
public class TreeSetApp {
public static void main(String[] args) {
// 初始化、逐个赋值
TreeSet<String> courseSet=new TreeSet<>();
System.out.println("courseSet:\t" + courseSet);
// size() 列表长度
System.out.println("size():\t" + courseSet.size());
// isEmpty() 是否为空
System.out.println("isEmpty():\t" + courseSet.isEmpty());
// contains() 是否包含
System.out.println("contains(\"Java\"):\t" + courseSet.contains("Java"));
// add() 插入
courseSet.add("Java");
System.out.println("add(\"Java\"):\t" + courseSet);
courseSet.add("Python");
System.out.println("add(\"Python\"):\t" + courseSet);
courseSet.add("Scala");
System.out.println("add(\"Scala\"):\t" + courseSet);
courseSet.add("Go");
System.out.println("add(\"Go\"):\t" + courseSet);
courseSet.add("PHP");
System.out.println("add(\"PHP\"):\t" + courseSet);
// remove() 删除
courseSet.remove("Scala");
System.out.println("remove(\"Scala\"):\t" + courseSet);
// descendingSet() 倒序
System.out.println("descendingSet():\t" + courseSet.descendingSet());
System.out.println("courseSet:\t" + courseSet);
// first() 查看首个元素
System.out.println("first():\t" + courseSet.first());
// last() 查看末尾元素
System.out.println("last():\t" + courseSet.last());
// foreach 遍历,实现了iterable接口
System.out.print("foreach():\t");
for (String course:courseSet){
System.out.print(course + " ");
}
System.out.println();
// iterator() 遍历,实现了iterator接口
System.out.print("iterator():\t");
Iterator<String> courseIterator = courseSet.iterator();
while (courseIterator.hasNext()){
System.out.print(courseIterator.next() + " ");
}
System.out.println();
}
}
5.2 结果
courseSet: []
size(): 0
isEmpty(): true
contains("Java"): false
add("Java"): [Java]
add("Python"): [Java, Python]
add("Scala"): [Java, Python, Scala]
add("Go"): [Go, Java, Python, Scala]
add("PHP"): [Go, Java, PHP, Python, Scala]
remove("Scala"): [Go, Java, PHP, Python]
descendingSet(): [Python, PHP, Java, Go]
courseSet: [Go, Java, PHP, Python]
first(): Go
last(): Python
foreach(): Go Java PHP Python
iterator(): Go Java PHP Python
6、HashMap
6.1 代码
package com.nash.java.core.ch01_collection;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Set;
/**
* 映射、关联数组 HashMap
* 无序、key不可重复、具有映射关系的集合。
*
* 1、Map中的key不可重复。
*/
public class HashMapApp {
public static void main(String[] args) {
// 初始化、逐个赋值
HashMap<Integer,String> courseMap= new HashMap<Integer,String>();
// size() 列表长度
System.out.println("size():\t" + courseMap.size());
// isEmpty() 是否为空
System.out.println("isEmpty():\t" + courseMap.isEmpty());
System.out.println("courseMap:\t" + courseMap);
// put() 插入
courseMap.put(101,"Java");
System.out.println("put(101,\"Java\"):\t" + courseMap);
courseMap.put(102,"Python");
System.out.println("put(102,\"Python\"):\t" + courseMap);
courseMap.put(103,"Scala");
System.out.println("put(103,\"Scala\"):\t" + courseMap);
courseMap.put(104,"Go");
System.out.println("put(104,\"Go\"):\t" + courseMap);
courseMap.put(105,"PHP");
System.out.println("put(105,\"PHP\"):\t" + courseMap);
// keySet() 查看key组成的集合
System.out.println("keySet():\t" + courseMap.keySet());
// values() 查看value组成的集合
System.out.println("values():\t" + courseMap.values());
// entrySet() 查看 key=value 组成的集合
System.out.println("entrySet():\t" + courseMap.entrySet());
// get() 根据key查询value
System.out.println("get(101):\t" + courseMap.get(101));
// remove() 删除
System.out.println("remove(101):\t" + courseMap.remove(101));
System.out.println("courseMap:\t" + courseMap);
// containsKey() 是否包含指定key
System.out.println("containsKey(102):\t" + courseMap.containsKey(102));
// containsValue() 是否包含指定value
System.out.println("containsValue(\"Python\"):\t" + courseMap.containsValue("Python"));
// iterator遍历key
Set<Integer> keys = courseMap.keySet();
System.out.print("iterator遍历key:\t");
Iterator<Integer> keyIterator = keys.iterator();
while (keyIterator.hasNext()){
System.out.print(keyIterator.next() + " ");
}
System.out.println();
// iterator遍历key
Collection<String> values = courseMap.values();
System.out.print("iterator遍历values:\t");
Iterator<String> valueIterator = values.iterator();
while (valueIterator.hasNext()){
System.out.print(valueIterator.next() + " ");
}
System.out.println();
// foreach遍历key、value
System.out.print("foreach遍历key、value:\t");
for (Integer key:keys){
System.out.print(key + "=" + courseMap.get(key) + " ");
}
}
}
6.2 结果
size(): 0
isEmpty(): true
courseMap: {}
put(101,"Java"): {101=Java}
put(102,"Python"): {101=Java, 102=Python}
put(103,"Scala"): {101=Java, 102=Python, 103=Scala}
put(104,"Go"): {101=Java, 102=Python, 103=Scala, 104=Go}
put(105,"PHP"): {101=Java, 102=Python, 103=Scala, 104=Go, 105=PHP}
keySet(): [101, 102, 103, 104, 105]
values(): [Java, Python, Scala, Go, PHP]
entrySet(): [101=Java, 102=Python, 103=Scala, 104=Go, 105=PHP]
get(101): Java
remove(101): Java
courseMap: {102=Python, 103=Scala, 104=Go, 105=PHP}
containsKey(102): true
containsValue("Python"): true
iterator遍历key: 102 103 104 105
iterator遍历values: Python Scala Go PHP
foreach遍历key、value: 102=Python 103=Scala 104=Go 105=PHP
7、TreeMap
7.1 代码
package com.nash.java.core.ch01_collection;
import java.util.*;
/**
* 映射、关联数组 TreeMap
* key有序、key不可重复、具有映射关系的集合。
*
* 1、Map中的key不可重复。
*/
public class TreeMapApp {
public static void main(String[] args) {
// 初始化、逐个赋值
TreeMap<Integer,String> courseMap= new TreeMap<Integer,String>();
// size() 列表长度
System.out.println("size():\t" + courseMap.size());
// isEmpty() 是否为空
System.out.println("isEmpty():\t" + courseMap.isEmpty());
System.out.println("courseMap:\t" + courseMap);
// put() 插入
courseMap.put(101,"Java");
System.out.println("put(101,\"Java\"):\t" + courseMap);
courseMap.put(102,"Python");
System.out.println("put(102,\"Python\"):\t" + courseMap);
courseMap.put(103,"Scala");
System.out.println("put(103,\"Scala\"):\t" + courseMap);
courseMap.put(104,"Go");
System.out.println("put(104,\"Go\"):\t" + courseMap);
courseMap.put(105,"PHP");
System.out.println("put(105,\"PHP\"):\t" + courseMap);
// descendingMap() 倒序
System.out.println("descendingMap():\t" + courseMap.descendingMap());
// descendingKeySet() 倒序查看key组成的集合
System.out.println("descendingKeySet():\t" + courseMap.descendingKeySet());
// headMap() 倒序查看key组成的集合
// keySet() 查看key组成的集合
System.out.println("keySet():\t" + courseMap.keySet());
// values() 查看value组成的集合
System.out.println("values():\t" + courseMap.values());
// entrySet() 查看 key=value 组成的集合
System.out.println("entrySet():\t" + courseMap.entrySet());
// get() 根据key查询value
System.out.println("get(101):\t" + courseMap.get(101));
// remove() 删除
System.out.println("remove(101):\t" + courseMap.remove(101));
System.out.println("courseMap:\t" + courseMap);
// containsKey() 是否包含指定key
System.out.println("containsKey(102):\t" + courseMap.containsKey(102));
// containsValue() 是否包含指定value
System.out.println("containsValue(\"Python\"):\t" + courseMap.containsValue("Python"));
// iterator遍历key
Set<Integer> keys = courseMap.keySet();
System.out.print("iterator遍历key:\t");
Iterator<Integer> keyIterator = keys.iterator();
while (keyIterator.hasNext()){
System.out.print(keyIterator.next() + " ");
}
System.out.println();
// iterator遍历key
Collection<String> values = courseMap.values();
System.out.print("iterator遍历values:\t");
Iterator<String> valueIterator = values.iterator();
while (valueIterator.hasNext()){
System.out.print(valueIterator.next() + " ");
}
System.out.println();
// foreach遍历key、value
System.out.print("foreach遍历key、value:\t");
for (Integer key:keys){
System.out.print(key + "=" + courseMap.get(key) + " ");
}
}
}
7.2 结果
size(): 0
isEmpty(): true
courseMap: {}
put(101,"Java"): {101=Java}
put(102,"Python"): {101=Java, 102=Python}
put(103,"Scala"): {101=Java, 102=Python, 103=Scala}
put(104,"Go"): {101=Java, 102=Python, 103=Scala, 104=Go}
put(105,"PHP"): {101=Java, 102=Python, 103=Scala, 104=Go, 105=PHP}
descendingMap(): {105=PHP, 104=Go, 103=Scala, 102=Python, 101=Java}
descendingKeySet(): [105, 104, 103, 102, 101]
keySet(): [101, 102, 103, 104, 105]
values(): [Java, Python, Scala, Go, PHP]
entrySet(): [101=Java, 102=Python, 103=Scala, 104=Go, 105=PHP]
get(101): Java
remove(101): Java
courseMap: {102=Python, 103=Scala, 104=Go, 105=PHP}
containsKey(102): true
containsValue("Python"): true
iterator遍历key: 102 103 104 105
iterator遍历values: Python Scala Go PHP
foreach遍历key、value: 102=Python 103=Scala 104=Go 105=PHP
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