java常用数据结构常用方法

秒速五厘米 2022-07-21 11:16 258阅读 0赞

**String/StringBuffer/ArrayList本质一样，底层都为数组，只不过动态静态的区别，方法也基本类似**

**1.String**

**![Center][]**

**![Center 1][]**

package com.ming.huawei;
    
    public class TestString {
    	
    	public static void main(String[] args) {
    		String a = " hello,paul234 ";
    		String b = " 你好啊 2 123";
    		String c = a.substring(2);
    		System.out.println(c);
    		String dString = a.substring(0, 3);
    		System.out.println(dString);
    		String eString = a.concat(b);
    		System.out.println(eString);
    		String fString = a.replace("e", "a");
    		System.out.println(fString);
    		int gString = a.indexOf("l");
    		System.out.println(gString);
    		String string = b.replaceAll("\\d", "d");
    		System.out.println(string);
    		System.out.println(a.charAt(2));
    		System.out.println(b.contains("e"));
    		char [] ds = a.toCharArray();
    		a.isEmpty();
    		a.indexOf("p");
    		a.lastIndexOf("l");
    		a.
    	}
    }

ello,paul234   
 he  
 hello,paul234  你好啊 2 123  
 hallo,paul234   
3  
 你好啊 d ddd  
e  
false

**2.StringBuffer**

public class TestStringBuffer {
    	public static void main(String[] args) {
    		String str = "hello, 12345";
    		StringBuffer sBuffer  = new StringBuffer(str);
    		sBuffer.append("678");
    		sBuffer.charAt(3);
    		int start=0;
    		int end=1;
    		sBuffer.delete(start, end);
    		sBuffer.deleteCharAt(3);
    		sBuffer.indexOf("l");
    		sBuffer.lastIndexOf("l");
    		int fromIndex=0;
    		sBuffer.indexOf(str, fromIndex);
    		sBuffer.replace(start, end, str);
    		sBuffer.reverse();
    		sBuffer.substring(1);
    		sBuffer.toString();
    		String str1 = " 12345 ";
    		StringBuffer sBuffer1  = new StringBuffer(str1);
    		
    		System.out.println(sBuffer1.length());
    	}
    }

3.HashMap

**![Center 2][]**

package com.ming.huawei;
    
    import java.util.HashMap;
    import java.util.Iterator;
    import java.util.LinkedList;
    import java.util.Map;
    import java.util.Map.Entry;
    import java.util.TreeMap;
    
    public class TestHashMap {
    	public static void main(String[] args) {
    		Map<String, Integer> map = new HashMap<String, Integer>();
    		Map<String, Integer> map1 = new TreeMap<String, Integer>();
    	    LinkedList<Integer> sIntegers = new LinkedList<Integer>();
    	    sIntegers.add(1);
    	    sIntegers.add(10200);
    	    sIntegers.add(6);
    	    sIntegers.add(78);
    	    sIntegers.sort(null);
    	    Object[] a = sIntegers.toArray();
    	    for(Object o:a){
    	    	System.out.print(o);
    	    }
    	    map.put("1", 3);
    	    map.put("3", 3);
    	    map.put("2", 5);
    	    map.put("4", 2);
    	   Iterator iterator = map.entrySet().iterator();
    	   while(iterator.hasNext()){
    		   Map.Entry<String, Integer> sEntry = (Entry<String, Integer>) iterator.next();
    		   System.out.println(sEntry.getKey()+""+sEntry.getValue());
    	   }
    	
    	}
    }

**3.ArrayList(可排序，正，逆序)--可传入数据--数组---string等**

**![Center 3][]**

package com.ming.huawei;
    
    import java.util.*;
    public class TSort{
        public static void main(String[]args){
            Scanner scan=new Scanner(System.in);
            ArrayList<String> list=new ArrayList<String>();
            int num=scan.hasNextLine()?Integer.parseInt(scan.nextLine()):0;
            while(--num>=0&&scan.hasNextLine()){
                 list.add(scan.nextLine());
            }
            Collections.sort(list);
    //        for(String str:set){
    //            System.out.println(str);
    //        }
            System.out.println("升序: ");
            for(int i = 0;i < list.size(); i ++){
            	
                System.out.print(" "+list.get(i));
            }
             System.out.println();
             System.out.println("降序: ");
            for(int i = list.size()-1;i >=0; i--){
               
                System.out.print(" "+list.get(i));
            }
        }
    }

6  
a  
c  
b  
f  
z  
a  
升序:   
 a a b c f z  
降序:   
 z f c b a a

**自定义排序：**

Collections.sort(imageList, new Comparator() { 
    public int compare(Object a, Object b) { 
    int orderA = Integer.parseInt( ( (Image) a).getSequence()); 
    int orderB = Integer.parseInt( ( (Image) b).getSequence()); 
    return orderA - orderB; 
    } 
    });

[Center]: /images/20220720/36dad4c304f6495a85ff41677ca24910.png
[Center 1]: /images/20220720/41a7ea6b54ca44a397fecca929962d97.png
[Center 2]: /images/20220720/c47035e64dcb4922b04837cd82bec0b7.png
[Center 3]: /images/20220720/19cb7cd3fe6b4db3997ecfca74e652e2.png