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

集合框架

 

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

listLambdasetmap

 *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);
    }