[Java 실습] 6. 자료구조와 컬랙션프레임워크

Q1. Collection 종합

 

package com.dinfree_1001;

import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;

public class CollectionTest {
	public static void main(String[] args) {
		
		//Create a new HashSet and add data
		Collection<String> c1=new HashSet<>();
		c1.add("one");
		c1.add("two");
		
		//Create a new List with two values
		Collection<String> c2=Arrays.asList("three", "four");
		Collection<String> c3=Collections.singleton("five");
		
		//add all data in c2, c3 to c1
		c1.addAll(c2);
		c1.addAll(c3);
		
		//get size of collection
		System.out.println("Size of c1 : "+ c1.size());
		
		//convert collection to array
		Object[] converted1 = c1.toArray();
		String[] converted2= c1.toArray(new String[c1.size()]);
		
		//print all data in collection using for loop
		for(String s:c1) {
			System.out.println(s);
		}
		
		//access and print all data in the array which converted from collection
		for(int i=0;i<converted2.length; i++) {
			System.out.println(converted2[i]);
		}
		
		//get Iterator object from collection
		Iterator iter=c1.iterator();
		while(iter.hasNext()) {
			System.out.println(iter.next());
		}
		
		//run specific code using every elements in the collection
		c1.forEach(System.out::println);
	}

}

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Q2. ArrayList, LinkedList 생성과 데이터다루기

package com.dinfree_1001;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;

public class ListTest {
	public static void main(String[] args) {
		//create new List
		List<String> l1 = new ArrayList<>();
		List<String> l2= Arrays.asList("one", "two");
		List<String> l3= List.of("three", "four");
		
		//add data to List
		l1.addAll(l2);
		l1.addAll(1, l3);
		l1.add("five");
		
		System.out.println("## element in List");
		System.out.println(l1);
		
		//create new LinkedList and add data
		LinkedList<String> llist=new LinkedList<>();
		llist.addAll(l2);
		llist.addAll(1,l3);
		llist.add("five");
		
		System.out.println("## element in LinkedList");
		System.out.println(l1);
		
		//access data with index
		System.out.println("## first element: "+ l1.get(0));
		System.out.println("## last index of three: "+ l1.lastIndexOf("three"));
		
		//change data in List
		l1.set(0, "zero");
		System.out.println("## after set (): element in LinkedList");
		System.out.println(l1);
		
		//Descending sort
		Collections.sort(l1);
		System.out.println("## Descending sort of l1");
		System.out.println(l1);
		
		//Ascending sort
		l1.sort(new Comparator<Object>() {
			@Override
			public int compare(Object o1, Object o2) {
				return o2.toString().compareTo(o1.toString());
			}
		});
		
		System.out.println("## Ascending sort of l1");
		System.out.println(l1);
		
		//Ascending sort with stream api
		System.out.println("## Ascending sort with stream api");
		l1.stream().sorted((o1,o2)->o2.toString().compareTo(o1.toString())).forEach(System.out::println);
		}
}

 

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Q3. Set 객체 생성과 데이터 다루기

package com.dinfree_1001;

import java.util.Arrays;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.TreeSet;

public class SetTest {
	public static void main(String[] args) {
		//create new Set
		Set<String> s1=new HashSet<>();
		Set<String> s2=Set.of("three", "four");
		
		//add element to Set
		s1.addAll(Arrays.asList("one","two"));
		s1.addAll(s2);
		s1.add("five");
		s1.add("two");
		s1.remove("five");
		
		System.out.println("## element in Set");
		System.out.println(s1);
		
		//print all elements using stream api
		s1.stream().forEach(System.out::println);
		
		System.out.println("## check exist element in set");
		System.out.println(s1.contains("one"));
		
		//create new LinkedHashSet and add elements
		Set<String> lset=new LinkedHashSet<>();
		lset.addAll(Arrays.asList("one","two","three","four"));
		lset.add("five");
		
		System.out.println("\n## element in LinkedHashSet");
		System.out.println(lset);
		
		//get Iterator from LinkedHashSet
		System.out.println("## print element using Iterator");
		Iterator<String> iter=lset.iterator();
		while(iter.hasNext()) {
			System.out.println(iter.next());
		}
		
		//create new TreeSet and add elements
		Set<Integer> tset=new TreeSet<>();
		tset.addAll(Arrays.asList(50,10,60,20));
		
		System.out.println("\n ## elements in TreeSet");
		System.out.println(tset);
		
		//Descending sort with stream api
		System.out.println("## Ascending sort with stream api");
        tset.stream().sorted((o1, o2) -> o2.toString().compareTo(o1.toString())).forEach(System.out::println);

	}

}

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Q4. Map

package com.dinfree_1001;

import java.util.HashMap;
import java.util.Map;

public class MapTest {
	public static void main(String[] args) {
		Map<String, String> map = new HashMap<>();
		map.put("1922876", "Apple iPhone");
		map.put("1922877", "Apple iPad");
		map.put("2136861", "Samsung Galaxy");
		map.put("2136863","Samsung Tablet");
		
		System.out.println("1922877: "+map.get("1922877"));
		
		System.out.println("--------");
		for(Map.Entry<String, String> entry:map.entrySet()){
		System.out.printf("%s:%s\n", entry.getKey(), entry.getValue());
		}
		
		System.out.println("--------");
		for(String s: map.keySet()) {
			System.out.printf("%s\n", s);
		}
		System.out.println("--------");
		for(String s:map.values()) {
			System.out.printf("%s\n",s);
		}
	}

}

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Q5. Map과 List

package com.dinfree_1001;

import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Scanner;

public class MapListTest {
	public static void main(String[] args) {
		List<Integer> s1 = Arrays.asList(95,89,93,87,94);
		List<Integer> s2=Arrays.asList(99,89,91,89,91);
		List<Integer> s3=Arrays.asList(93,81,95,88,89);
		
		Map<String, List<Integer>> student = new HashMap<>();
		student.put("홍길동", s1);
		student.put("김사랑", s2);
		student.put("아무개", s3);
		
		Scanner scan = new Scanner(System.in);
		System.out.println("## 성적 조회할 이름을 입력하세요: ");
		String input = scan.next();
		
		int total=0;
		for(int s: student.get(input)) {
			total+=s;
		}
		
		System.out.printf("총점: %d, 평균: %d", total, total/5);
}
}