前言：
回顾Java基础部分中集合的一些常用操作。JDK的版本为1.8，使用单元测试运行程序。
1.Collection接口的常用方法：
package com.yan.collection;
import org.junit.Test;
import java.util.*;
public class CollectionTest {
@Test
public void test() {
Collection coll = new ArrayList();
coll.add(123);
coll.add(456);
coll.add(new String("Tom"));
coll.add(false);
coll.add(new Person("Jerry", 20));
boolean contains = coll.contains(123);
System.out.println(contains); //true
System.out.println(coll.contains(new String("Tom"))); //true
Collection coll1 = Arrays.asList(123, 45678);
System.out.println(coll.containsAll(coll1)); //false
//3.remove(Object obj)：从当前集合中移除obj元素
coll.remove(123);
System.out.println(coll);
//4.removeAll(Collection coll2)：差集：从当前集合中移除coll2中所有的元素
Collection coll2 = Arrays.asList(456, false);
coll.removeAll(coll2);
System.out.println(coll);
//5.retainAll():交集:获取当前集合和coll3的交集，并返回给当前集合
Collection coll3 = Arrays.asList(new String("Tom"));
coll.retainAll(coll3);
System.out.println(coll);
}
@Test
public void test1() {
Collection coll = new ArrayList();
coll.add(123);
coll.add(456);
coll.add(new String("Tom"));
coll.add(false);
coll.add(new Person("Jerry", 20));
//6.hashCode()返回当前对象的哈希值
System.out.println(coll.hashCode());
//7.集合-->数组：toArray()
Object[] arr = coll.toArray();
for (int i = 0; i < arr.length; i++) {
System.out.println(arr[i]);
}
//8.数组-->集合：调用Arrays类的静态方法asList()
List list = Arrays.asList(new String[]{"AA", "BB", "CC"});
System.out.println(list);
List arr1 = Arrays.asList(new int[]{1, 2, 3}); //视作一个元素
System.out.println(arr1.size()); //1个元素
List arr2 = Arrays.asList(new Integer[]{1, 2, 3}); //视作三个元素
System.out.println(arr2.size()); //3个元素
//9.iterator():返回Iterator接口的实例，用于遍历集合元素.
Iterator iterator = coll.iterator();
while (iterator.hasNext()) {
//iterator.next()：取出迭代器的元素
//iterator.hasNext()：判断是否还有元素
System.out.println(iterator.next());
}
}
@Test
public void test2() {
Collection coll = new ArrayList();
coll.add(123);
coll.add(456);
coll.add(new String("Tom"));
coll.add(false);
coll.add(new Person("Jerry", 20));
//remove():删除集合中“Tom”
Iterator iterator = coll.iterator();
while (iterator.hasNext()) {
Object obj = iterator.next();
if ("Tom".equals(obj)) {
iterator.remove();
}
}
//遍历集合方式一
iterator = coll.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
//遍历集合方式二，同时也可以遍历数组
//for(集合元素的类型 局部遍历 ：集合对象)
for(Object o :coll){
System.out.println(o);
}
}
}
2.List接口的常用方法：
package com.yan.collection;
import org.junit.Test;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class ListTest {
@Test
public void test(){
ArrayList list = new ArrayList();
list.add(123);
list.add(456);
list.add(new String("Tom"));
list.add("AS");
list.add(new Person("Jerry",19));
System.out.println(list);
//1. void add(int index, Object ele):在index位置插入ele元素
list.add(1,"BE");
System.out.println(list);
//2. Boolean addAll(int index, Collection ele):从index位置开始将ele中所有元素添加进来
List arr = Arrays.asList(1, 2, 3);
list.addAll(arr);
System.out.println(list.size()); //9
//3. object get(int index):获取指定index位置的元素
System.out.println(list.get(0));
//4. int indexOf(Object obj):返回obj在集合中首次出现的位置,如不存在，则返回-1
int index = list.indexOf(456);
System.out.println(index);
//5. int lastIndexOf(Object obj):返回obj在当前集合中末次出现的位置
System.out.println(list.lastIndexOf("AS"));
//6. Object remove(int index):移除指定index位置的元素，并返回此元素
Object remove = list.remove(0);
System.out.println(remove);
System.out.println(list);
//7. Object set(int index, Object ele):设置指定index位置的元素ele
list.set(1,"CS");
System.out.println(list);
//8. List subList(int fromIndex, int toIndex):返回从fromIndex到toIndex位置的子集合
List subList = list.subList(2, 4);
System.out.println(subList);
}
}
3.Set接口的常用方法：
package com.yan.collection;
import org.junit.Test;
import java.util.*;
public class SetList {
@Test
public void test(){
Set set = new HashSet();
set.add(123);
set.add(456);
set.add(789);
set.add("AA");
set.add("BB");
set.add(new Person("Tom",18));
set.add(new Person("Jack",19));
Iterator iterator = set.iterator();
while (iterator.hasNext()){
System.out.println(iterator.next());
}
}
@Test
public void test1(){
TreeSet set = new TreeSet();
//向TreeSet中添加数据，要求是相同类的对象。
// set.add(923);
// set.add(456);
// set.add(789);
//
// Iterator iterator = set.iterator();
// while (iterator.hasNext()){
// System.out.println(iterator.next());
// }
set.add(new Person("Tom",14));
set.add(new Person("Jack",18));
set.add(new Person("Shawn",19));
set.add(new Person("Nie",16));
set.add(new Person("Nie",20));
Iterator iterator = set.iterator();
while (iterator.hasNext()){
System.out.println(iterator.next());
}
}
@Test
public void test2(){
Comparator com = new Comparator() {
//按照年龄从小到大排序
@Override
public int compare(Object o1, Object o2) {
if(o1 instanceof Person && o2 instanceof Person){
Person person1 = (Person) o1;
Person person2 = (Person) o2;
return Integer.compare(person1.getAge(), person2.getAge());
}else{
throw new RuntimeException("输入的数据类型不匹配");
}
}
};
TreeSet set1 = new TreeSet(com);
set1.add(new Person("Tom",14));
set1.add(new Person("Jack",18));
set1.add(new Person("Shawn",19));
set1.add(new Person("Nie",16));
set1.add(new Person("Nie",20));
Iterator iterator = set1.iterator();
while (iterator.hasNext()){
System.out.println(iterator.next());
}
}
}
4.Map接口的常用方法：
package com.yan.collection;
import org.junit.Test;
import java.util.*;
public class MapTest {
@Test
public void test(){
HashMap map = new HashMap();
map.put("AA",123);
map.put(789,234);
map.put("CC",391);
System.out.println(map); // {AA=123, CC=391, 789=234}
HashMap map1 = new HashMap();
map1.put("DD",563);
map1.put("EE",189);
map.putAll(map1);
System.out.println(map); // {AA=123, CC=391, DD=563, EE=189, 789=234}
Object value = map.remove("CC");
System.out.println("删除的元素的值: "+value); // 391
System.out.println(map); // {AA=123, DD=563, EE=189, 789=234}
map.clear();
System.out.println(map.size()); // 0
}
@Test
public void test1(){
HashMap map = new HashMap();
map.put("AA",123);
map.put(789,234);
map.put("CC",391);
System.out.println(map.get("AA")); //123
boolean isExist = map.containsKey("CC");
System.out.println(isExist); //true
boolean value = map.containsValue(123);
System.out.println(value); //true
map.clear();
System.out.println(map.isEmpty()); //true
}
@Test
public void test2(){
HashMap map = new HashMap();
map.put("AA",123);
map.put(789,234);
map.put("CC",391);
//遍历所有的key
Set set = map.keySet();
Iterator iterator = set.iterator();
while (iterator.hasNext()){
System.out.println(iterator.next());
}
System.out.println();
//遍历所有的value
Collection values = map.values();
for (Object o:values){
System.out.println(o);
}
System.out.println();
//遍历所有的key-value对
//方式一:entrySet()
Set entrySet = map.entrySet();
Iterator iterator1 = entrySet.iterator();
while (iterator1.hasNext()){
Object o = iterator1.next();
//entrySet集合中的元素都是entry
Map.Entry entry = (Map.Entry) o;
System.out.println(entry.getKey()+"--->"+entry.getValue());
}
System.out.println();
//方式二:通过key来遍历所有的键值对
Set setKey = map.keySet();
Iterator iterator2 = setKey.iterator();
while (iterator2.hasNext()){
Object key = iterator2.next();
Object value = map.get(key);
System.out.println(key+"---"+value);
}
}
@Test
//自然排序,其排序方法已经在Person类里重写,按姓名从大到小排序
public void test3(){
TreeMap map = new TreeMap();
Person p1 = new Person("Tom",18);
Person p2 = new Person("Shawn",19);
Person p3 = new Person("Jerry",17);
Person p4 = new Person("Caroline",16);
map.put(p1,96);
map.put(p2,98);
map.put(p3,97);
map.put(p4,93);
Set entrySet = map.entrySet();
Iterator iterator1 = entrySet.iterator();
while (iterator1.hasNext()){
Object o = iterator1.next();
//entrySet集合中的元素都是entry
Map.Entry entry = (Map.Entry) o;
System.out.println(entry.getKey()+"--->"+entry.getValue());
}
}
@Test
//定制排序
public void test4(){
TreeMap map = new TreeMap(new Comparator() {
@Override
public int compare(Object o1, Object o2) {
if(o1 instanceof Person && o2 instanceof Person){
Person per1 = (Person) o1;
Person per2 = (Person) o2;
//按年龄从小到大
return Integer.compare(per1.getAge(),per2.getAge());
}
throw new RuntimeException("输入的类型不匹配");
}
});
Person p1 = new Person("Tom",18);
Person p2 = new Person("Shawn",19);
Person p3 = new Person("Jerry",17);
Person p4 = new Person("Caroline",16);
map.put(p1,96);
map.put(p2,98);
map.put(p3,97);
map.put(p4,93);
Set entrySet = map.entrySet();
Iterator iterator1 = entrySet.iterator();
while (iterator1.hasNext()){
Object o = iterator1.next();
//entrySet集合中的元素都是entry
Map.Entry entry = (Map.Entry) o;
System.out.println(entry.getKey()+"--->"+entry.getValue());
}
}
}
5.Collections工具类的使用：
package com.yan.collection;
import org.junit.Test;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
public class CollectionsTest {
@Test
public void test(){
List list = new ArrayList();
list.add(123);
list.add(34);
list.add(63);
list.add(8763);
list.add(8763);
list.add(8763);
list.add(8763);
list.add(10);
System.out.println(list);
//Collections.shuffle(list);
//Collections.sort(list);
//Collections.swap(list, 1, 2);
//System.out.println(list);
int frequency = Collections.frequency(list,8763);
System.out.println(frequency);
}
@Test
public void test1(){
List list = new ArrayList();
list.add(123);
list.add(34);
list.add(63);
list.add(8763);
//报异常: IndexOutOfBoundsException: Source does not fit in dest
// List dest = new ArrayList();
// Collections.copy(dest, list);
//正确的写法:
List
6.集合举例使用的Person类：
package com.yan.collection;
import java.util.Objects;
public class Person implements Comparable{
private String name;
private int age;
public Person() {
}
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Person{" +
"name='" + name + ''' +
", age=" + age +
'}';
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Person person = (Person) o;
return age == person.age && Objects.equals(name, person.name);
}
@Override
public int hashCode() {
return Objects.hash(name, age);
}
@Override
//按照姓名从大到小排序，年龄从小到大
public int compareTo(Object o) {
if(o instanceof Person){
Person person = (Person) o;
int compare = -this.name.compareTo(person.name);
if(compare!=0){
return compare;
}else {
return Integer.compare(this.age, person.age);
}
}else{
throw new RuntimeException("输入的类型不匹配");
}
}
}
