Java中List去重

爱被打了一巴掌 2022-09-08 03:53 182阅读 0赞

import java.util.ArrayList;
    import java.util.HashSet;
    import java.util.Iterator;
    import java.util.List;
    import java.util.Set;
    import java.util.stream.Collectors;
    
    public class Test {
        
    
    	public static void main(String[] args) {
        
    		
    		List<String> list = new ArrayList<String>();
    		
    		list.add("1001A410000000PS6PI3");
    		list.add("1001A410000000PS6WK7");
    		list.add("1001A410000000PS6PI3");
    		list.add("1001A410000000PS6W77");
    		
    		System.out.println(removeDuplicate1(list));
    //		System.out.println(removeDuplicate2(list));
    //		System.out.println(removeDuplicate3(list));
    //		System.out.println(removeDuplicate4(list));
    //		System.out.println(removeDuplicate5(list));
    		 
    	}
    
    	/**
    	 * 方法一： Stream 去重：list.stream().distinct()
    	 * @param list
    	 * @return
    	 */
    	private static List<String> removeDuplicate1(List<String> list) {
        
    		List<String> newList = (List) list.stream().distinct().collect(Collectors.toList());
    		return newList;
    	}
    	
    	/**
    	 * 方法二：通过 HashSet 剔除重复元素(会改变原有顺序)
    	 * @param list
    	 * @return
    	 */
    	private static List<String> removeDuplicate2(List<String> list) {
        
    		Set<String> tempSet = new HashSet<String>(list);
    		list.clear();
    		list.addAll(tempSet);
    		return list;
    	}
    	
    	/**
    	 * 方法三：删除 ArrayList 中重复元素，保持顺序
    	 * @param list
    	 * @return
    	 */
    	private static List<String> removeDuplicate3(List<String> list) {
        
    		
    		Set<String> tempSet = new HashSet<String>();
    		List<String> newList = new ArrayList<>();
    		
    		for (Iterator iter = list.iterator(); iter.hasNext(); ) {
        
    	        String next = (String) iter.next();
    	        if (tempSet.add(next)) {
        
    	            newList.add(next);
    	        }
    	    }
    		return newList;
    	}
    	
    	/**
    	 * 方法四：遍历 list，用 tempList.contain()，不存在 add
    	 * @param list
    	 * @return
    	 */
    	private static List<String> removeDuplicate4(List<String> list) {
        
    		List<String> tempList = new ArrayList<>();
    		
    		for (int i = 0; i < list.size(); i++) {
        
    			if (!tempList.contains(list.get(i))) {
        
    				tempList.add(list.get(i));
    			}
    		}
    		return tempList;
    	}
    	
    	/**
    	 * 方法五：循环 list 中的所有元素然后删除重复(会改变原有顺序)
    	 * @param list
    	 * @return
    	 */
    	private static List<String> removeDuplicate5(List<String> list) {
        
    		for (int i = 0; i < list.size(); i++) {
        
    	        for (int j = list.size() - 1; j > i; j--) {
        
    	           if (list.get(i).equals(list.get(j))) {
        
    	                list.remove(list.get(i));
    	            }
    	        }
    	    }
    		return list;
    	}
    }