java collections 集合基础学习 ArrayList，LinkedList, HashSet, TreeSet, HashMap, Stack,Queue,PriorityQueue

怼烎@ 2022-09-24 12:29 189阅读 0赞

collections 集合基础用法

包括ArrayList，LinkedList, HashSet, TreeSet, HashMap, Stack,Queue,PriorityQueue的方法和用法。

上代码：

package com.yuxin.learn;
    import java.util.*;
    
    
    public class Main {
    	
    
    	private static void display(Iterator<String> it) {
    		System.out.println("call display():");
    		// TODO Auto-generated method stub
    		while(it.hasNext()){
    			String s = it.next();
    			System.out.print(s+" ");
    		}
    		System.out.println();
    	}
    	
    	
    	public static void print(Object l){
    		System.out.println(l);
    	}
    	
    	public static void main(String[] args){
    		/** 
    		 * 1. List Set Queue 继承自Collection
    		 *	(1).ArrayList继承自List
    		 *		1) ArrayList的所有方法
    		 */
    		
    		Collection<Integer> alt_Int = new ArrayList<Integer>();
    		alt_Int.add(0);
    		alt_Int.add(2);
    		Random rand = new Random();
    		for(int i=1;i<100;i++){
    			alt_Int.add(rand.nextInt(30));
    		}
    		System.out.println(alt_Int);
    		
    		/** 
    		 * 1. List Set Queue 继承自Collection
    		 *	(1).ArrayList继承自List
    		 *		1) ArrayList的所有方法
    		 */
    		//List<String> altString = Arrays.asList("dog","cat","pig");
    		print("****************   Part 1  ArrayList  Method ***********");
    		ArrayList<String> altString = new ArrayList<String>();
    		altString.add("dog");
    		altString.add("cat");
    		altString.add("pig");
    		print("1 pets:"+ altString);
    		altString.add("rat");
    		print("2 add rat:"+ altString);
    		// a.contiains(b)
    		print("3 contains rat?:"+altString.contains("rat"));
    		
    		ArrayList<pet> altObj = new ArrayList<pet>();
    		pet p1 = new pet("objcat");
    		altObj.add(p1);
    		pet p2 = new pet("objdog");
    		altObj.add(p2);
    		
    		//add()
    		print("4 objcat indexof:"+altObj.indexOf(p1));
    		pet p3 = new pet("obj3");
    		altObj.add(p3);
    		pet p4 = new pet("obj4");
    		altObj.add(p4);
    		pet p5 = new pet("obj5");
    		altObj.add(p5);
    		print ("5 objArrayList:"+altObj);
    		//subList()
    		List<pet> sub = altObj.subList(2, 5);
    		print("6 sub Arraylist:"+sub);
    		//containsAll()
    		print("7 containsAll: "+ altObj.containsAll(sub));
    		Collections.shuffle(sub,rand);
    		print("8 shuffle sub Arraylist:"+sub);
    		
    		List<pet> sub2 = new ArrayList<pet>();
    		
    		//asList()
    		sub2=Arrays.asList(altObj.get(1),altObj.get(3));
    		print("9 .get sub: "+ sub2);
    		
    		List<pet> temp = new ArrayList<pet>();
    		temp = altObj;
    		//a.removeAll(b)
    		print("10 before removeAll: "+temp);
    		temp.removeAll(sub2);
    		print("11 after removeAll in sub2:"+temp);
    		
    		//a.clear()
    		temp.clear();
    		print("12 after clear:"+temp);
    		
    		//a.isEmpty()
    		print("13 isEmpty():"+temp.isEmpty());
    	
    		Object[] o = altObj.toArray();
    		print("14 toArray():"+o);
    		//iterator
    		Iterator<pet> it = altObj.iterator();
    		print("15 iterator: ");
    		while(it.hasNext()){
    			pet p = it.next();
    			System.out.print(p+". ");
    		}
    		print(" ");
    		display(altString.iterator());
    		
    		
    		
    		print("****************   Part 2 LinkList  Method ***********");
    		LinkedList<String> objLinkList = new LinkedList<String>(Arrays.asList("cat","rat","dot","bird","ant"));
    		print("1 objLinkList:"+objLinkList);
    		//getFirst()
    		print("2 getFist():"+objLinkList.getFirst());
    		//element()
    		print("3 element():"+objLinkList.element());
    		//peek()
    		print("4 peek()"+objLinkList.peek());
    		//remove()
    		//String r = objLinkList.element();
    		//objLinkList.remove(r);
    		print("5 remove()"+objLinkList.remove());
    		//LinkedList<String> ListTemp = objLinkList;
    		//removeFirst()
    		print("6 removeFirst():"+objLinkList.removeFirst());
    		print("7 after remove"+objLinkList);
    		//addFirst()
    		objLinkList.addFirst("Rat");
    		print("8 after addFist():"+objLinkList);
    		//offer()
    		objLinkList.offer("OfferA");
    		print("9 after offer():"+objLinkList);
    		//addLast
    		objLinkList.addLast("AddLastB");
    		print("10 after addLast:"+objLinkList);
    		objLinkList.removeLast();
    		print("10 after removeLast:"+objLinkList);
    		
    		
    		print("****************   Part 3 Stack  Method ***********");
    		//print("Impement a Stack using LinkedList:");
    		Stack<String> stk = new Stack<String>();
    		String str = "I Love Java progaraming!";
    		print("store sentence \"I Love Java progaraming!\" in a stack and pop out:");
    		for(String s:str.split(" ")){
    			stk.push(s);
    		}
    		while(!stk.isEmpty()) print( stk.pop()+" ");
    		
    		System.out.println();
    		print("****************   Part 4 Set  Method ***********");
    		/**
    		 * Set 不保存重复元素
    		 *   可以选择HashSet或者TreeSet实现，专门对快速查找进行优化。
    		 *   HashSet 保存顺序没有规律（散列存储），TreeSet 红-黑树存储
    		 *   LinkedHashSet 使用了散列存储，但使用链表维护元素插入顺序。
    		 */
    		Set<String> set1 = new HashSet<String>();
    		//Collections.addAll()
    		print("Collections.addAll():");
    		Collections.addAll(set1, "A B C D E F G H I J K L M".split(" "));
    		print(set1);
    		set1.add("N");
    		//contiains
    		print("1 contains() H:"+set1.contains("H"));
    		print("2 contains() Z:"+set1.contains("Z"));
    		Set<String> set2 = new HashSet<String>();
    		Collections.addAll(set2, "G H I J".split(" "));
    		print("3 containsAll()  set2 in set1:"+set1.containsAll(set2));
    		set1.remove("H");
    		print("4 after remove H  whether contains H:"+set1.contains("H"));
    		print("5 after remove H,set1 containsAll set2?:"+set1.containsAll(set2));
    		Collections.addAll(set1, "X Y Z".split(" "));
    		print("6 'X Y Z'added to set1:"+set1);
    		print("7 TreeSet:");
    		//rand.nextInt
    		Set<Integer> altIntSort = new TreeSet<Integer>();
    		for(int i=1;i<100;i++){
    			altIntSort.add(rand.nextInt(30));
    		}
    		System.out.println(altIntSort);
    		
    		System.out.println();
    		print("****************   Part 5 Map  Method ***********");
    		/**
    		 * 用Map求产生的随机数的次数 key->随机数，value->次数
    		 * 1）获得value 用 m.get(key)方法
    		 * 2）存入map 用 m.put(key,value)方法
    		 */
    		print("Generate 1000 integer, calculate the frequency.");
    		Map<Integer,Integer> map1 = new HashMap<Integer,Integer>();
    		for(int i=0;i<1000;i++){
    			int r = rand.nextInt(20);
    			Integer fre = map1.get(r);
    			map1.put(r,fre==null?1:fre+1);
    		}
    		print(map1);
    		
    		print("hashmap:");
    		Map<String,String> petMap = new HashMap<String,String>();
    		petMap.put("yx", "dog");
    		petMap.put("hx", "cat");
    		petMap.put("cc", "rat");
    		//containsKey
    		print("containsKey: yx:"+petMap.containsKey("yx"));
    		print("containsKey: yxx:"+petMap.containsKey("yxx"));
    		print("containsValue: cat:"+petMap.containsValue("cat"));
    		//keySet
    		print("keySet:"+petMap.keySet());
    		//values
    		print("valueSet:"+petMap.values());
    		//map<person,List<pet>>;
    		
    		
    		System.out.println();
    		print("****************   Part 6 Queue Method ***********");
    		/**
    		 * 通过将LinkedList向上转型实现Queue.(窄化了LinkedList的访问权限)
    		 * LinkedList提供了方法支持队列的行为，可作为队列的一种实现。
    		 * 
    		 */
    		Queue<Character> queS = new LinkedList<Character>();
    		for(char c:"Life is beautiful~".toCharArray()){
    			queS.offer(c);
    		}
    		print("1 String to CharArray offer into queue: "+queS);
    		//element
    		print("2 element:"+queS.element());
    		//peek
    		print("3 peek:"+queS.peek());
    		//poll
    		print("4 poll:"+queS.poll());
    		print("5 after poll:"+queS);
    		//addLast
    		queS.add('*');
    		print("6 after addLast:"+queS);
    		
    		print("PriorityQueue:");
    		/**
    		 * 
    		 * 当调用offer()方法添加对象，对象会在队列中被排序
    		 */
    		List<String> str1 = Arrays.asList("I think nothing is imporsible".split(" "));
    		PriorityQueue<String> PriQueS = new PriorityQueue<String>(str1);
    		print("1 priority que:"+PriQueS);
    		PriorityQueue<String> PriQueS_reverse = new PriorityQueue<String>(str1.size(),Collections.reverseOrder());
    		PriQueS_reverse.addAll(str1);
    		print("2 after add all, priority que _reverse:"+PriQueS_reverse);
    		String str2 = "I think nothing is imporsible";
    		List<Character> Allch = new ArrayList<Character>();
    		for(char c:str2.toCharArray()){
    			Allch.add(c);
    		}
    		PriorityQueue<Character> PriQueAll = new PriorityQueue<Character>();
    		PriQueAll.addAll(Allch);
    		print("3 PriorityQueue all char:"+PriQueAll);
    		//对于字母去重复，注意使用HashSet
    		Set<Character> charSet = new HashSet<Character>();
    		for(char c:str2.toCharArray()){
    			charSet.add(c);
    		}
    		PriorityQueue<Character> PriQueC = new PriorityQueue<Character>(charSet);
    		print("4 PriorityQueue single char:"+PriQueC);
    		//输出环境变量
    		Main m =new Main();
    		EnvironmentVar evn = m.new EnvironmentVar();
    		evn.output();
    		
    		print("基本异常");
    		//Object t1 = null;
    		//if(t1==null)throw new NullPointerException();
    		print("如果直接抛出了异常，程序就会停在这，而加入catch后，会继续运行。");
    		try{
    			Object t1 = null;
    			if(t1==null)throw new NullPointerException();
    		}catch(NullPointerException e){
    			print("catched a execption!");
    		}
    		print("Exception finished");//加入捕捉异常后，才会执行到这
    		
    		
    		print("****************   Part 7 String Method ***********");
    		String str0="We are Chinese.";
    		print("str0"+str0);
    		//length()
    		print("1 length:"+str0.length());
    		//charAt()
    		print("2 charAt:"+str0.charAt(4));
    		char[] charArr = new char[20];
    		for(int i=0;i<20;i++) charArr[i]='0';
    		//getChars
    		str0.getChars(3, 7,charArr,4);
    		for(char c:charArr)System.out.print(c);
    		System.out.println();
    		//valueOf
    		print("3 valueOf(change charArray into String method):"+String.valueOf(charArr));
    		String str3="Chinese";
    		print("str3:"+str3);
    		//equals
    		print("4 equals:"+str0.equals(str3));
    		//compareTo
    		print("5 compareTo:"+str0.compareTo(str3));
    		//contains
    		print("6 contains:"+str0.contains(str3));
    		//StringBuffer
    		StringBuffer sb = new StringBuffer("We are Chinese.");
    		//contentEquals
    		print("7 contentEquals:"+str0.contentEquals(sb));
    		//equalsIgnoreCase
    		print("8 equalsIgnoreCase:"+str0.equalsIgnoreCase(str3));
    		//regionMatches
    		print("9 regionMatches(区域对比):"+str0.regionMatches(7, str3, 0, 4));
    		//startsWith
    		print("10 startsWith:"+str0.startsWith("W"));
    		//endsWith
    		print("11 endsWith:"+str0.endsWith("."));
    		//indexOf
    		print("12 indexOf(i):"+str0.indexOf("i"));
    		print("13 indexOf(t):"+str0.indexOf("t"));
    		//lastIndexOf
    		print("14 lastIndexOf(i)从后向前搜索:"+str0.lastIndexOf("i"));
    		//subString
    		print("15 subString:"+str0.substring(3));
    		//concat
    		print("16 concat:"+str0.concat("aaaaaaa"));
    		//replace
    		print("17 replace:"+str0.replace("n", "sd"));
    		//toLowerCase
    		print("18 toLowerCase:"+str0.toLowerCase());
    		//toUpperCase
    		print("19 toUpperCase:"+str0.toUpperCase());
    		//trim
    		print("20 trim:"+str0.trim());
    		//valueOf
    		/**
    		 * String.valueOf(boolean b) : 将 boolean 变量 b 转换成字符串 
    			String.valueOf(char c) : 将 char 变量 c 转换成字符串 
    			String.valueOf(char[] data) : 将 char 数组 data 转换成字符串 
    			String.valueOf(char[] data, int offset, int count) : 
    			将 char 数组 data 中 由 data[offset] 开始取 count 个元素 转换成字符串 
    			String.valueOf(double d) : 将 double 变量 d 转换成字符串 
    			String.valueOf(float f) : 将 float 变量 f 转换成字符串 
    			String.valueOf(int i) : 将 int 变量 i 转换成字符串 
    			String.valueOf(long l) : 将 long 变量 l 转换成字符串 
    			String.valueOf(Object obj) : 将 obj 对象转换成 字符串, 等于 obj.toString() 
    		 */
    		print("20 valueOf(转化为字符串):"+String.valueOf(354));
    		
    		/**
    		 * intern 这个方法 返回字符串对象的规范化表示形式，当调用 intern 方法时
    		 * ，如果池已经包含一个等于此 String 对象的字符串（该对象由 equals(Object) 
    		 * 方法确定），则返回池中的字符串。否则，将此 String 对象添加到池中，并且
    		 * 返回此 String 对象的引用。这时候c和d就是相等的。
    		 */
    		print("21 intern:判断目前的string对象是否已经存在于常量池，存在则返回存在对象的引用");
    		String a =  "b" ;   
    	    String b =  "b" ;   
    	    System.out.print( a == b);  
    	    String c = "d" ;  
    	    String d = new String( "d" ).intern() ;   
    	    System.out.println( c == d);  
    	    
    		String s1 = "ab123" ;  
            String s2 = new String( "ab123" ) ;  
            System.out.println( s1 == s2 );   
            String s3 = s2.intern() ;   
            System.out.println( s1 == s3 ) ; 
            
            int a1=324;
            print("格式化输出：");
            System.out.printf("a1:%d\n",a1);
            System.out.format("a1\\:%d\n",a1);
            
    		
    	}
    
    	class EnvironmentVar {
    		/**
    		 * System.getenv()返回一个Map，entrySet()产生一个有Map.Entry的元素构成的Set，
    		 * 并且Set是一个Iterable，因此她可以用于foreach循环。
    		 */
    		//public void EnvironmentVar(){}
    		public void output(){
    			System.out.println("output environment var:");
    			for(Map.Entry entry:System.getenv().entrySet()){
    				System.out.println(entry.getKey()+":"+entry.getValue());
    			}
    		}
    	}
    
    	
    }

实现上面的代码正常运行，另外还需要一个类：

package com.yuxin.learn;	
    
    public class pet{
    	private String pet;
    	public pet(String string) {
    		// TODO Auto-generated constructor stub
    		pet=string;
    	}
    }