JAVA__List、Set、M

List ——有序、可重复

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
public class Main {
public static void main(String[] args) {

List list = new ArrayList();
list.add("qwe");
list.add(123456);
list.add(789456);
list.add("@#$%^&*");
for (int i = 0; i < list.size(); i++) {
System.out.println(list.get(i));
}
System.out.println("========");

for (Object x : list) {
System.out.println(x);
}
System.out.println("========");

Iterator it = list.iterator();//迭代器
while (it.hasNext()) {
Object x = it.next();
System.out.println(x);
}
}
}

Set——无序、不可重复 HashSet

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
public class Main {
public static void main(String[] args) {

Set set = new HashSet();
set.add("qwe");
set.add(123456);
set.add(789456);
set.add("@#$%^&*");
set.add("qwe");
// for (int i = 0; i < set.size(); i++) {
// System.out.println(set.get(i));
// }//不可行
System.out.println("========");

for (Object x : set) {
System.out.println(x);
}
System.out.println("========");

Iterator it = set.iterator();// 迭代器
while (it.hasNext()) {
Object x = it.next();
System.out.println(x);
}
}
}

Map——映射、无序、不可重复

import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class Main {
public static void main(String[] args) {

Map map = new HashMap();
map.put("a", 97);// 被覆盖
map.put(12.3, 78.9);
map.put("&*^%$#@", 520134);
map.put(521, "mmp");
map.put("a", 77);

System.out.println("Key----------------------------------------------");
Set K = map.keySet();
Iterator it = K.iterator();// 迭代器
while (it.hasNext()) {
Object k = it.next();
Object v = map.get(k);
System.out.println(k + "---" + v);
}
 
System.out.println("values----------------------------------------------");
Collection V = map.values();
Iterator it1 = V.iterator();
while (it1.hasNext()) {
Object v = it1.next();
System.out.println(v);
}

System.out.println("entry-----------------------------------------------------");
Set E = map.entrySet();
Iterator it2 = E.iterator();
while (it2.hasNext()) {
Map.Entry<Object, Object> e = (Map.Entry<Object, Object>) it2.next();
System.out.println(e);
}
}
}

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