Java ——集合框架 list lambda set map 遍历方法数据结构

本节重点思维导图

有序无序：元素放入的顺序与取出的顺序是否一致，一致即为有序，不一致即无序。

List：允许重复、有序
ArrayList：长度可变的数组，遍历速度快
LinkedList：链表：添加删除节点速度快

import java.util.ArrayList;

import java.util.Date;

import java.util.List;

public class Demo {

    public static void main(String[] args) {

        List list = new ArrayList();

        System.out.println("--------"+list.toString());//add

        list.add("aa");

        list.add(1234);

        list.add(true);

        list.add(new Date());

        list.add(1234);

        list.add(3.14);

        System.out.println(list.get(0) + "   --     " + list.get(3));

        System.out.println(list.size());

        System.out.println(list);

        System.out.println(list.toString());

        for (Object obj : list) {

            System.out.println(obj);

        }

        list.remove(0);// 根据下标移除

        list.clear();

        System.out.println(list.size());

    }

}

结果：

--------[]

aa   --     Fri May 31 15:07:45 CST 2019

6

[aa, 1234, true, Fri May 31 15:07:45 CST 2019, 1234, 3.14]

[aa, 1234, true, Fri May 31 15:07:45 CST 2019, 1234, 3.14]

aa

1234

true

Fri May 31 15:07:45 CST 2019

1234

3.14

0

泛型

import java.util.ArrayList;

import java.util.Date;

import java.util.Iterator;

import java.util.List;

public class Demo {

    public static void main(String[] args) {

                        List<String> list = new ArrayList<>();

                        list.add("1234");

                        list.add("true");

                        list.add("aaaa");

                        list.add("aaaa");

                        list.add("bbbb");

                        list.add("dddd");  

                        String e3 = list.get(3);

                        System.out.println(e3);

                        System.out.println(list.get(3));

                        int size = list.size();

                        System.out.println(size);  

                        for (String item : list) {

                            System.out.println(item);

                        }  

                        System.out.println("--------------------------");

                        // Iterator迭代器

                        Iterator<String> iterator = list.iterator();

                        while (iterator.hasNext()) {// 判断是否还有下一个元素，有的话返回true

                            String next = iterator.next();// 取出元素，同时将指针指向当前位置

                            System.out.println(next);

                        }

                    }

}

结果：

aaaa

aaaa

6

1234

true

aaaa

aaaa

bbbb

dddd

--------------------------

1234

true

aaaa

aaaa

bbbb

dddd

list\Lambda\set\map

*lambda

public static void main(String[] args) {

        List<String> list = new ArrayList<>();

        list.add("zhangsan");

        list.add("lisi");

        list.add("zhangsan");

        list.add("wanger");

        list.add("mazi");

        list.add("wanger");

        list.stream().forEach(element->System.out.println(element));

        System.out.println();

        list.forEach(item -> System.out.println(item));

        System.out.println();

        list.forEach(System.out::println);

        //将List中所有的元素变成大写字母后再逆序输出

        System.out.println();

        for(int i =list.size()-1;i>=0;i--) {

            String item = list.get(i);

            item = item.toUpperCase();

            System.out.println(item);

        }

        System.out.println();

        list.stream().map(item->item.toUpperCase())//映射：依次拿出List中的每一个元素进行映射

            .forEach(System.out::println);

        //输出List中每一个元素的前两个字符

        System.out.println();

        list.stream().map(item->item.substring(0, 2))

            .forEach(System.out::println);

        //只输出List中长度大于4的元素

        System.out.println();

        list.stream().filter(item->item.length()>4)

            .forEach(System.out::println);

        //去除重复

        System.out.println();

        list.stream().distinct().forEach(System.out::println);

        //将Stream转换成List

        System.out.println();

        List<String> collect = list.stream().collect(Collectors.toList());

        System.out.println(collect);

    }

*set

public static void main(String[] args) {

        Set<String> set  = new HashSet<>();

        set.add("zhangsan");

        set.add("lis");

        set.add("zhangsan");

        set.add("wanger");

        set.add("mazi");

        set.add("wanger");

        for(String item : set) {

            System.out.println(item);

        }

        System.out.println();

        Iterator<String> iterator = set.iterator();

        while(iterator.hasNext()) {

            System.out.println(iterator.next());

        }

        System.out.println();

        set.forEach(System.out::println);

    }

示例：学习set判断元素是否相等

public class Dept {

    private int deptno;

    private String dname;

    private String loc;

    public Dept() {

        super();

    }

    public Dept(int deptno, String dname, String loc) {

        super();

        this.deptno = deptno;

        this.dname = dname;

        this.loc = loc;

    }

    public int getDeptno() {

        return deptno;

    }

    public void setDeptno(int deptno) {

        this.deptno = deptno;

    }

    public String getDname() {

        return dname;

    }

    public void setDname(String dname) {

        this.dname = dname;

    }

    public String getLoc() {

        return loc;

    }

    public void setLoc(String loc) {

        this.loc = loc;

    }

    @Override

    public int hashCode() {

        return 234;

    }

    @Override

    public boolean equals(Object obj) {

        return true;

    }

    @Override

    public String toString() {

        return "Dept [deptno=" + deptno + ", dname=" + dname + ", loc=" + loc + "]";

    }

}

    public static void main(String[] args) {

        Set<Dept> set = new HashSet<>();

        set.add(new Dept());

        set.add(new Dept());

        set.add(new Dept(10,"sales","new york"));

        set.add(new Dept(20,"research","chicago"));

        System.out.println(set.size());

        set.forEach(System.out::println);

    }

*map

键值对

public static void main(String[] args) {

        Map<String, Integer> data = new HashMap<>();

        data.put("a", 1);

        data.put("b", 2);

        data.put("c", 3);

        data.put("d", 4);

        System.out.println(data.get("a"));

        Set<String> keySet = data.keySet();

        keySet.forEach(System.out::println);

        Collection<Integer> values = data.values();

        values.forEach(item->System.out.print(item+" "));

        System.out.println();

        Set<Entry<String, Integer>> entrySet = data.entrySet();

        for(Entry<String, Integer> item: entrySet) {

            System.out.println(item.getKey()+" "+item.getValue());

        }

        data.forEach((k,v)->System.out.println(k+" : "+v));;

    }

遍历方法

快捷键：

代码格式化：ctrl+sfhit+f

自动提示：alt+?

抽取变量：alt+shift+L

复习总结

Arrays

public static void main(String[] args) {

        String[] data = { "zhangsan", "lisi", "wanger", "mazi","qianwu","zhaoliu" };

        List<String> asList = Arrays.asList(data);

        System.out.println(asList);

        System.out.println(data);

        System.out.println(Arrays.toString(data));

        int binarySearch = Arrays.binarySearch(data, "lisi");

        System.out.println(binarySearch);

        //对数组进行扩容

        String[] copyOf = Arrays.copyOf(data, data.length + 4);

        for (String item : copyOf)

            System.out.println(item);

        String[] copyOfRange = Arrays.copyOfRange(data, 2, 4);

        System.out.println(Arrays.toString(copyOfRange));

        String[] copyOf2 = Arrays.copyOf(data, data.length);

        boolean equals = Arrays.equals(data,copyOf2);//比较两个数组的内容是否相等

        System.out.println(equals);

        boolean[] bol = new boolean[8];

        System.out.println(Arrays.toString(bol));

        Arrays.fill(bol,true);

        System.out.println(Arrays.toString(bol));

        Arrays.sort(data);

        System.out.println(Arrays.toString(data));

        System.out.println("--------------------");

        //匿名内部类

        Comparator<String> c = new Comparator<String>() {

            @Override

            public int compare(String o1, String o2) {

                return o2.length()-o1.length();

            }

        };

        Arrays.sort(data,c);

        System.out.println(Arrays.toString(data));

        data = new String[]{ "zhangsan", "lisi", "wanger", "mazi","qianwu","zhaoliu" };

        Arrays.sort(data,(o1,o2)->o2.length()-o1.length());

        System.out.println(Arrays.toString(data));

    }

collections

public static void main(String[] args) {

        List<String> list = new ArrayList<>();

        Collections.addAll(list,"zhangsan", "lisi","zhangsan","wanger","zhangsan","mazi");

        System.out.println(list);

        int binarySearch = Collections.binarySearch(list, "lisi3");

        System.out.println(binarySearch);

        int binarySearch2 = Collections.binarySearch(list, "wanger", (o1,o2)->o1.length()-o2.length());

        System.out.println(binarySearch2);

        Collections.sort(list, new Comparator<String>() {

            @Override

            public int compare(String o1, String o2) {

                return o1.length()-o2.length();

            }

        });

        System.out.println(list);

        Collections.shuffle(list);

        System.out.println(list);

        Collections.sort(list, (o1,o2)->o1.length()-o2.length());;

        System.out.println(list);

        Collections.replaceAll(list, "zhangsan", "***");

        System.out.println(list);

        Collections.swap(list, 1, 3);

        System.out.println(list);

        Collections.reverse(list);

        System.out.println(list);

    }

list

public static void main(String[] args) {

        List<String> list = new ArrayList<>();

        Collections.addAll(list,"zhangsan", "lisi","wanger","mazi");

        for(int i =0;i<list.size();i++){

            System.out.println(list.get(i));

        }

        for(String item : list){

            System.out.println(item);

        }

        Iterator<String> iterator = list.iterator();

        while(iterator.hasNext()){

            System.out.println(iterator.next());

        }

        ListIterator<String> listIterator = list.listIterator();

        while(listIterator.hasNext()){

            System.out.println(listIterator.next());

        }

        list.forEach(item->System.out.println(item));

        list.forEach(System.out::println);

    }

set

public static void main(String[] args) {

        Set<String> set = new HashSet<>();

        set.add("aa");

        set.add("bb");

        set.add("cc");

        set.add("dd");

        for(String item : set){

            System.out.println(item);

        }

        Iterator<String> iterator = set.iterator();

        while(iterator.hasNext()){

            System.out.println(iterator.next());

        }

        set.forEach(item->System.out.println(item));

        set.forEach(System.out::println);

    }

map

原则：将map变为set

public static void main(String[] args) {

        Map<Integer,Goods> map = new HashMap<>();

        map.put(111, new Goods(111,"aaa",1,"aaaaaaaaaaa"));

        map.put(222, new Goods(222,"bbb",2,"bbbbbbbbbbbbb"));

        map.put(333, new Goods(333,"ccc",3,"ccccccccccccc"));

        map.put(444, new Goods(444,"ddd",4,"dddddddddddd"));

        Set<Integer> keySet = map.keySet();

        for(Integer key : keySet){

            System.out.println(key+" : "+map.get(key));

        }

        Set<Entry<Integer, Goods>> entrySet = map.entrySet();

        for(Entry<Integer, Goods> item : entrySet){

            System.out.println(item.getKey()+" "+item.getValue());

        }

        map.forEach((k,v)->System.out.println(k+" :: "+v));;

    }

扩展：

public static void main(String[] args) {

        List<String> list = Arrays.asList("zhangsan","lisi","wanger","mazi");

        Collections.sort(list, new Comparator<String>() {

            @Override

            public int compare(String o1, String o2) {

                return o1.length() - o2.length();

            }

        });

        System.out.println(list);

        System.out.println("-------------");

        list.forEach(item->System.out.println(item+" "+item.hashCode()));

        list.sort((o1,o2)->{

            return o1.hashCode()- o2.hashCode();

        });

        list.forEach(System.out::println);

    }

巴特西

Java ——集合框架 list lambda set map 遍历方法数据结构

最新文章

热门文章

巴特西

Java ——集合框架 list lambda set map 遍历方法 数据结构

最新文章

热门文章

Java ——集合框架 list lambda set map 遍历方法数据结构