List<String> mutableList = new ArrayList<>(Arrays.asList("A", "B"));
List<String> unmodifiable = Collections.unmodifiableList(mutableList);

// 嘗試修改將拋出異常
unmodifiable.add("C"); // UnsupportedOperationException

// 但原始集合修改會(huì)影響"不可變"視圖
mutableList.add("C"); 
System.out.println(unmodifiable); // 輸出[A, B, C]  ? 實(shí)際已改變

List<String> immutableList = List.of("Java", "Kotlin", "Scala");
Set<Integer> immutableSet = Set.of(1, 2, 3);
Map<String, Integer> immutableMap = Map.of("One", 1, "Two", 2);

// 所有修改操作均拋出異常
immutableList.add("Go");  // UnsupportedOperationException
immutableSet.remove(1);   // UnsupportedOperationException

// 構(gòu)建器模式
ImmutableList<String> list = ImmutableList.<String>builder()
    .add("Spring")
    .addAll(existingList)
    .build();

// 工廠方法
ImmutableSet<Integer> set = ImmutableSet.copyOf(mutableSet);
ImmutableMap<String, Integer> map = ImmutableMap.of("key1", 1, "key2", 2);

// 拒絕null值
ImmutableList.of(null); // 立即拋出NullPointerException

// Java 10的ImmutableCollections實(shí)現(xiàn)
static final class ListN<E> extends AbstractImmutableList<E> {
    private final E[] elements; // 使用final數(shù)組存儲(chǔ)
}

public void add(int index, E element) {
    throw new UnsupportedOperationException();
}

static <E> List<E> listCopy(Collection<? extends E> coll) {
    return coll.isEmpty() ? List.of() 
        : new ImmutableCollections.ListN<>(coll.toArray());
}

// 1. 元素對(duì)象本身仍可變
List<Date> dates = List.of(new Date());
dates.get(0).setTime(0); // 成功修改日期對(duì)象

// 2. 大集合創(chuàng)建
Set.of(...); // 超過16元素需改用Map.ofEntries()

import java.util.Iterator;
import java.util.List;

public class ImmutableDemo1 {
    public static void main(String[] args) {
        /**
         * 創(chuàng)建不可變的List集合
         * "張三","李四","王五","趙六"
         */

        //一旦創(chuàng)建完畢之后，是無法進(jìn)行修改的，在下面的代碼中，只能進(jìn)行查詢操作
        List<String> list = List.of("張三", "李四", "王五", "趙六");

        //用list調(diào)用get方法
        System.out.println(list.get(0));
        System.out.println(list.get(1));
        System.out.println(list.get(2));
        System.out.println(list.get(3));

		//增強(qiáng)for遍歷
        for (String s : list) {
            System.out.println(s);
        }

        //迭代器遍歷
        Iterator<String> it = list.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }

        //lambda表達(dá)式遍歷
        list.forEach( s -> System.out.println(s));

        //方法引用遍歷
        list.forEach(System.out::println);
        
		
    }
}

list.set(0,"aaa");
list.add("zzz");
list.remove("張三");

import java.util.Iterator;
import java.util.Set;

public class ImmutableDemo2 {
    public static void main(String[] args) {
        /**
         * 創(chuàng)建不可變的Set集合
         * "張三","李四","王五","趙六"
         */

        //一旦創(chuàng)建完畢之后，是無法進(jìn)行修改的，在下面的代碼中，只能進(jìn)行查詢操作
        Set<String> set = Set.of("張三","李四","王五","趙六");


        //增強(qiáng)for遍歷
        for (String s : set) {
            System.out.println(s);
        }

        //迭代器遍歷
        Iterator<String> it = set.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }

        //lambda表達(dá)式遍歷
        set.forEach( s -> System.out.println(s));

        //方法引用遍歷
        set.forEach(System.out::println);
    }
}

set.remove("王五");
set.add("aaa");

Set<String> set = Set.of("張三","李四","王五","趙六","趙六"); 
//此處我們創(chuàng)建了一個(gè)帶有重復(fù)元素的Set集合，重復(fù)元素為趙六

import java.util.Map;
import java.util.Set;

public class ImmutableDemo3 {
    public static void main(String[] args) {
        /**
         * 創(chuàng)建不可變的Map集合
         *
         * "張三","南京","李四","北京","王五","上海","趙六","廣州"
         */
        //一旦創(chuàng)建完畢之后，是無法進(jìn)行修改的，在下面的代碼中，只能進(jìn)行查詢操作
        Map<String, String> map = Map.of("張三", "南京", "李四", "北京", "王五", "上海", "趙六", "廣州");


        Set<String> keys = map.keySet();

        //增強(qiáng)for遍歷
        for (String key : keys) {
            String value = map.get(key);
            System.out.println(key + "=" + value);
        }

        //entrySet方法遍歷
        Set<Map.Entry<String, String>> entries = map.entrySet();
        for (Map.Entry<String, String> entry : entries) {
            String key = entry.getKey();
            String value = entry.getValue();
            System.out.println(key + "=" + value);
        }
    }
}