List 列表常用操作

初始化列表

package org.onepiece;

import java.lang.String;
import java.util.*;
import java.util.stream.Collectors;

public class Main {

    public static void main(String[] args) {

        //1
        List<String> emptyList = new ArrayList<>();
        System.out.println(emptyList.getClass().getName());//java.util.ArrayList
        System.out.println(emptyList);//[]


        //2
        String[] array = {"AA", "BB", "cc", "DD", "EE"};
        List<String> list = new ArrayList<>(Arrays.asList(array));
        System.out.println(list.getClass().getName());//java.util.ArrayList
        System.out.println(list);//[AA, BB, cc, DD, EE]


        //3
        List<String> newList = new ArrayList<>(Arrays.asList("AA", "BB", "cc", "DD", "EE"));
        System.out.println(newList.getClass().getName());//java.util.ArrayList
        System.out.println(newList);//[AA, BB, cc, DD, EE]

    }
}

//比较 -> 引用地址
System.out.println(list == newList); //false

//比较 -> 值
System.out.println(list.equals(newList));//true

 

 

新增(add)、删除(remove)、随机访问(get) 元素

package org.onepiece;

import java.lang.String;
import java.util.*;

public class Main {

    public static void main(String[] args) {

        List<String> list = new ArrayList<>();
        System.out.println(list);//[]


        //添加元素
        list.add("one");
        list.add("two");
        list.add("three");
        list.add("four");
        System.out.println(list);//[one, two, three, four]


        //删除元素
        list.remove("five");
        System.out.println(list);//[one, two, three, four]

        list.remove("four");
        System.out.println(list);//[one, two, three]


        //删除指定位置的元素
        list.remove(1);
        System.out.println(list);//[one, three]


        //访问随机元素
        String str = list.get(0);
        System.out.println(str);//one

    }
}

 

 列表判断操作方法

package org.onepiece;

import java.lang.String;
import java.util.*;

public class Main {

    public static void main(String[] args) {

        List<String> list = new ArrayList<>();
        System.out.println(list);//[]


        //列表是否为空
        boolean isEmpty = list.isEmpty();
        System.out.println(isEmpty);//true

        //列表大小
        int size = list.size();
        System.out.println(size);//0

        System.out.println(list.contains("one"));//false
        System.out.println(list.contains("123"));//false


        //添加元素
        list.add("one");
        list.add("two");
        list.add("three");
        list.add("123");


        isEmpty = list.isEmpty();
        System.out.println(isEmpty);//false

        size = list.size();
        System.out.println(size);//4

        System.out.println(list.contains("one"));//true
        System.out.println(list.contains("123"));//true
        System.out.println(list.contains("one123"));//false


        //转化成数组
        String[] array = list.toArray(new String[list.size()]);
        System.out.println(array.length);//4
        System.out.println(Arrays.toString(array));//[one, two, three, 123]

    }
}

 

遍历列表

package org.onepiece;

import java.lang.String;
import java.util.*;

public class Main {

    public static void main(String[] args) {

        List<String> list = new ArrayList<>(Arrays.asList("one", "two", "three"));
        System.out.println(list);//[one, two, three]

        //1：for
        for (int i = 0; i < list.size(); i++) {
            System.out.print(list.get(i) + " ");
        }
        //one two three
　　　　 

　　　　 //2：foreach
        for (String str : list) {
            System.out.print(str + " ");
        }
        //one two three


　　　　 //3：lambda表达式
        list.forEach(s -> {
            System.out.print(s + " ");
        });
        //one two three
    }
}

//备注：
//如果 list.size()==0，则它不会进入循环遍历的方法块里面 { } 

 

列表其它操作

package org.onepiece;

import java.lang.String;
import java.util.*;

public class Main {

    public static void main(String[] args) {

        List<String> list = new ArrayList<>(Arrays.asList("one", "two", "three", "four", "five"));
        System.out.println(list);//[one, two, three, four, five]


　　　　 //removeIf：用于删除满足某个条件的元素

        //删掉含有"o"字符的字符串
        //[one,two,four]
        list.removeIf(s -> {
            return s.contains("o");
        });
        System.out.println(list);//[three, five]


        //删掉字符串长度大于的字符串
        //[three]
        list.removeIf(s -> {
            return s.length() > 4;
        });
        System.out.println(list);//[five]


        //删掉含有"f"字符的字符串
        //[five]
        list.removeIf(s -> s.contains("f"));
        System.out.println(list);//[]



        list.add("AA");
        System.out.println(list);//[AA]


        //addAll：将other1集合中的所有元素添加到list列表
        //并集
        Collection<String> other1 = Arrays.asList("AA", "BB", "CC");
        list.addAll(other1);
        System.out.println(list);//[AA, AA, BB, CC]


        //removeAll：list列表中删除other2集合中存在的元素
        //差集
        Collection<String> other2 = Arrays.asList("AA", "BB");
        list.removeAll(other2);
        System.out.println(list);//[CC]


        list.add("dd");
        System.out.println(list);//[CC, dd]


        //retainAll：list列表中删除所有与other3集合中的不同元素
        //交集
        Collection<String> other3 = Arrays.asList("CC", "dd", "efg");
        list.retainAll(other3);
        System.out.println(list);//[CC, dd]


        //清空所有元素
        list.clear();
        System.out.println(list);//[]
    }
}