Java基础之Collections常用方法演示

骑猪看日落 2022-12-11 09:24 228阅读 0赞

package cn.itcast.p2.toolclass.collections.demo;
    
    import java.util.ArrayList;
    import java.util.Collections;
    import java.util.Comparator;
    import java.util.List;
    import java.util.TreeSet;
    
    import cn.itcast.p2.comparator.ComparatorByLength;
    
    public class CollectionsDemo {
        
    
    	/**
    	 * @param args
    	 */
    	public static void main(String[] args) {
        
    
    		
    		/*
    		 * Collections：是集合框架的工具类。
    		 * 里面的方法都是静态的。
    		 * 
    		 * 
    		 */
    		
    		demo_4();
    	}
    	
    	public static void demo_4() {
        
    		List<String> list = new ArrayList<String>();
    		
    		list.add("abcde");
    		list.add("cba");
    		list.add("zhangsan");
    		list.add("zhaoliu");
    		list.add("xiaoqiang");
    		
    		System.out.println(list);
    //		Collections.replaceAll(list, "cba", "nba"); // set(indexOf("cba"),"nba");
    		Collections.shuffle(list);
    //		Collections.fill(list, "cc");
    		System.out.println(list);
    	}
    
    	public static void demo_3() {
        
    		/*
    		TreeSet<String> ts = new TreeSet<String>(new Comparator<String>(){
    
    			@Override
    			public int compare(String o1, String o2) {
    				
    				int temp = o2.compareTo(o1);
    				return temp;
    			}
    			
    		});
    		*/
    		TreeSet<String> ts = new TreeSet<String>(Collections.reverseOrder(new ComparatorByLength()));	
    		
    		ts.add("abc");
    		ts.add("hahaha");
    		ts.add("zzz");
    		ts.add("aa");
    		ts.add("cba");
    		
    		System.out.println(ts);
    		
    	}
    
    	public static void demo_2(){
        
    		List<String> list = new ArrayList<String>();
    		
    		list.add("abcde");
    		list.add("cba");
    		list.add("aa");
    		list.add("zzz");
    		list.add("cba");
    		list.add("nbaa");
    //		Collections.sort(list);
    		System.out.println(list);
    		
    //		int index = Collections.binarySearch(list, "cba");		
    //		System.out.println("index="+index);
    		
    		//获取最大值。
    		String max = Collections.max(list,new ComparatorByLength());
    		System.out.println("max="+max);
    	}
    	
    	
    	
    	public static void demo_1(){
        
    		
    		List<String> list = new ArrayList<String>();
    		
    		list.add("abcde");
    		list.add("cba");
    		list.add("aa");
    		list.add("zzz");
    		list.add("cba");
    		list.add("nbaa");
    		System.out.println(list);
    		
    		
    		//对list集合进行指定顺序的排序。
    //		Collections.sort(list);
    //		mySort(list);
    //		mySort(list,new ComparatorByLength());
    		Collections.sort(list,new ComparatorByLength());
    		System.out.println(list);
    	}
    	public static <T> void mySort(List<T> list,Comparator<? super T> comp){
        
    		
    		for (int i = 0; i < list.size()-1; i++) {
        
    			
    			for (int j = i+1; j < list.size(); j++) {
        
    				
    				if(comp.compare(list.get(i), list.get(j))>0){
        
    					
    //					T temp = list.get(i);
    //					list.set(i, list.get(j));
    //					list.set(j, temp);
    					Collections.swap(list, i, j);
    					
    				}
    			}
    		}
    	}
    	
    	
    	public static <T extends Comparable<? super T>> void mySort(List<T> list){
        
    		
    		for (int i = 0; i < list.size()-1; i++) {
        
    			
    			for (int j = i+1; j < list.size(); j++) {
        
    				
    				if(list.get(i).compareTo(list.get(j))>0){
        
    					
    //					T temp = list.get(i);
    //					list.set(i, list.get(j));
    //					list.set(j, temp);
    					Collections.swap(list, i, j);
    					
    				}
    			}
    		}
    	}
    
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg1MzY2OQ_size_16_color_FFFFFF_t_70_pic_center_pic_center]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg1MzY2OQ_size_16_color_FFFFFF_t_70_pic_center_pic_center]: /images/20221123/85f306892f5e4029a7bc88ae0d0eda89.png