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黑马程序员Java个人总结

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目录

1、泛型

        1、泛型的定义格式:

        1.1 泛型的好处:

         2、泛型类:

        3、泛型方法:

        4、泛型接口:

        5、类型通配符:

        6、可变参数:

         7、可变参数的使用:

 2、Map集合

        1、Map集合的概述和特点

         2、Map集合的基本功能

         3、Map集合的获取功能

        4、Map集合的遍历

        4.1遍历方法一

        4.2遍历方法二

        5、HashMap集合案例

        5.1案例一

        5.2案例二

        6、集合嵌套

        6.1集合嵌套之ArrayList嵌套HashMap

        6.2集合嵌套之HashMap嵌套ArrayList

        7、统计字符串每个字符出现的次数

         8、Collections的概述和使用

         9、用ArrayList集合存储学生并遍历


 

1、泛型

        1、泛型的定义格式:

        1.1 泛型的好处:

         2、泛型类:

        //泛型类

//泛型类
public class Generic<T>{
    private T t;

    public T getT(){
        return t;
    }
    public void setT(T t){
        this.t =t;
    }
}

        //测试类

//测试类
public class work11{
    public static void main(String[] args){
        Student s = new Student();
        Generic<String> g = new Generic<>();
        g.setT("中国");
        System.out.println(g.getT());          //中国
        System.out.println("----------");
        Generic<Integer> g1 = new Generic<>();
        g1.setT(100);
        System.out.println(g1.getT());         //100
        System.out.println("----------");
        Generic<Boolean> g2 = new Generic<>();
        g2.setT(true);
        System.out.println(g2.getT());         //true
    }
}

        3、泛型方法:

        //Generic类中定义泛型方法

//Generic类
public class Generic{
    public <T> void show(T t){
        System.out.println(t);
    }
}

        //测试类

public class work11{
    public static void main(String[] args){
        Generic g = new Generic();
        g.show("中国");         //中国
        g.show(100);           //100
        g.show(true);          //true
        g.show(12.34);         //12.34
    }
}

        4、泛型接口:

        //接口

public interface Generic<T>{
    void show(T t);
}

        //实现接口的类

public class GenericImpl<T> implements Generic<T>{
    @Override
    public void show(T t) {
        System.out.println(t);
    }
}

        //测试类

public class work11{
    public static void main(String[] args){
        Generic<String> g = new GenericImpl<>();
        g.show("中国");                   //中国
        Generic<Integer> g2 = new GenericImpl<>();
        g2.show(100);                    //100
        Generic<Boolean> g3 = new GenericImpl<>();
        g3.show(true);                   //true
    }
}

        5、类型通配符:

import java.util.*;

public class work11{
    public static void main(String[] args){
        List<?> list1 = new ArrayList<Object>();
        List<?> list2 = new ArrayList<Number>();
        List<?> list3 = new ArrayList<Integer>();
        System.out.println("-----------");
        //List<? extends Number> list4 = new ArrayList<Object>();     会报错
        List<? extends Number> list4 = new ArrayList<Number>();
        List<? extends Number> list5 = new ArrayList<Integer>();
        System.out.println("-----------");
        //List<? super Number> list6 = new ArrayList<Integer>();      会报错
        List<? super Number> list6 = new ArrayList<Object>();
        List<? super Number> list7 = new ArrayList<Number>();
    }
}

        6、可变参数:

public class work11{
    public static void main(String[] args){
        System.out.println(sum(10,20));                  //30
        System.out.println(sum(10,20,30));               //60
        System.out.println(sum(10,20,30,40));            //100
        System.out.println(sum(10,20,30,40,50));         //150
        System.out.println(sum(10,20,30,40,50,60));      //210
    }
    /*
        public static int sum(int b,int...a){
            int sum = b;
            for(int i:a){
                sum += i;
            }
            return sum;
        }
     */
    public static int sum(int...a){
        int sum = 0;
        for(int i:a){
            sum += i;
        }
        return sum;
    }
}

         7、可变参数的使用:

import java.util.*;

public class work11{
    public static void main(String[] args){
        List<String> list1 = Arrays.asList("hello","world","java");
//        list1.add("javaee");         //会报错
//        list1.remove("hello");       //会报错
        list1.set(1,"javaee");
        System.out.println(list1);     //[hello, javaee, java]
        System.out.println("------------");
        List<String> list2 = List.of("hello","world","java");
//        list1.add("javaee");         //会报错
//        list1.remove("hello");       //会报错
//        list1.set(1,"javaee");       //会报错
        System.out.println(list2);     //[hello, world, java]
        System.out.println("------------");
        Set<String> set = Set.of("hello","world","java");
//        Set<String> set = Set.of("hello","world","java","hello");  //会报错
//        list1.add("javaee");         //会报错
//        list1.remove("hello");       //会报错
//        list1.set(1,"javaee");       //会报错
        System.out.println(set);       //[world, java, hello]
    }
}

 2、Map集合

        1、Map集合的概述和特点

import java.util.*;

public class work11{
    public static void main(String[] args){
        Map<Integer,String> map = new HashMap<>();
        //put方法,键不存在时为添加,如果键存在时为修改
        map.put(1,"风清扬");
        map.put(2,"天山果佬");
        map.put(3,"橙留香");
        map.put(3,"菠萝吹雪");
        System.out.println(map);    //{1=风清扬, 2=天山果佬, 3=菠萝吹雪}
    }
}

         2、Map集合的基本功能

import java.util.*;

public class work11{
    public static void main(String[] args){
        //创建Map对象
        Map<Integer,String> map = new HashMap<>();
        //put方法,键值不存在时为添加,如果键值存在时为修改
        map.put(1,"风清扬");
        map.put(2,"天山果佬");
        map.put(3,"菠萝吹雪");
        System.out.println(map);    //{1=风清扬, 2=天山果佬, 3=菠萝吹雪}

        System.out.println(map.remove(1));     //风清扬
        System.out.println(map.remove(1));     //null
        System.out.println(map);    //{2=天山果佬, 3=菠萝吹雪}

        System.out.println(map.containsKey(2));   //true
        System.out.println(map.containsValue("菠萝吹雪"));  //true

        System.out.println(map.size());     //2

        map.clear();       //移除Map集合中的所有键值对
        System.out.println(map.isEmpty());   //true
    }
}

         3、Map集合的获取功能

import java.util.*;

public class work11{
    public static void main(String[] args){
        //创建Map对象
        Map<Integer,String> map = new HashMap<>();
        //put方法,键值不存在时为添加,如果键值存在时为修改
        map.put(1,"风清扬");
        map.put(2,"天山果佬");
        map.put(3,"菠萝吹雪");

        System.out.println(map.get(1));  //风清扬
        System.out.println(map.get(4));  //null

        Set<Integer> set = map.keySet();
        for(Integer i:set){
            System.out.println(i);       //1 2 3
        }

        Collection<String> c = map.values();
        for(String s:c){
            System.out.println(s);      //风清扬 天山果佬 菠萝吹雪
        }
    }
}

        4、Map集合的遍历

        4.1遍历方法一

import java.util.*;

public class work11{
    public static void main(String[] args){
        //创建Map对象
        Map<Integer,String> map = new HashMap<>();
        //put方法,键值不存在时为添加,如果键值存在时为修改
        map.put(1,"风清扬");
        map.put(2,"天山果佬");
        map.put(3,"菠萝吹雪");
        //获取键的集合
        Set<Integer> set = map.keySet();
        //用加强for循环遍历
        for(Integer i:set){
            //根据键获取相应的值
            String s = map.get(i);
            System.out.println(i+","+s);
        }
    }
}

        4.2遍历方法二

import java.util.*;

public class work11{
    public static void main(String[] args){
        //创建Map对象
        Map<Integer,String> map = new HashMap<>();
        //put方法,键值不存在时为添加,如果键值存在时为修改
        map.put(1,"风清扬");
        map.put(2,"天山果佬");
        map.put(3,"菠萝吹雪");
        //获取键值对的集合
        Set<Map.Entry<Integer,String>> entrySet = map.entrySet();
        //用加强for循环遍历
        for(Map.Entry<Integer,String> me:entrySet){
            int i = me.getKey();
            String s = me.getValue();
            System.out.println(i+","+s);
        }
    }
}

        5、HashMap集合案例

        5.1案例一

//测试类
import java.util.*;

public class work11{
    public static void main(String[] args){
        //创建HashMap集合
        HashMap<String,Student> hm = new HashMap<>();
        //创建学生对象
        Student s1 = new Student("风清扬",30);
        Student s2 = new Student("天山果佬",35);
        Student s3 = new Student("菠萝吹雪",33);
        hm.put("itheima001",s1);
        hm.put("itheima002",s2);
        hm.put("itheima003",s3);
        //创建所有键的集合
        Set<String> set = hm.keySet();
        //用加强for循环遍历
        for(String s:set){
            Student ss = hm.get(s);
            System.out.println(s+","+ss.getName()+","+ss.getAge());
        }
        System.out.println("----------");
        //创建所有键值对的集合
        Set<Map.Entry<String,Student>> entrySet = hm.entrySet();
        //用加强for循环遍历
        for(Map.Entry<String,Student> me:entrySet){
            String s = me.getKey();
            Student ss = me.getValue();
            System.out.println(s+","+ss.getName()+","+ss.getAge());
        }
    }
}

//学生类
public class Student{
    private String name;
    private int age;

    public Student(){}
    public Student(String name,int age){
        this.name = name;
        this.age = age;
    }

    public void setName(String name){
        this.name = name;
    }
    public String getName(){
        return name;
    }

    public void setAge(int age){
        this.age = age;
    }
    public int getAge(){
        return age;
    }
}

        5.2案例二

//测试类
import java.util.*;

public class work11{
    public static void main(String[] args){
        //创建HashMap集合
        HashMap<Student,String> hm = new HashMap<>();
        //创建学生对象
        Student s1 = new Student("风清扬",30);
        Student s2 = new Student("天山果佬",35);
        Student s3 = new Student("菠萝吹雪",33);
        hm.put(s1,"itheima001");
        hm.put(s2,"itheima002");
        hm.put(s3,"itheima003");
        //创建所有键的集合
        Set<Student> set = hm.keySet();
        //用加强for循环遍历
        for(Student s:set){
            String ss = hm.get(s);
            System.out.println(ss+","+s.getName()+","+s.getAge());
        }
        System.out.println("----------");
        //创建所有键值对的集合
        Set<Map.Entry<Student,String>> entrySet = hm.entrySet();
        //用加强for循环遍历
        for(Map.Entry<Student,String> me:entrySet){
            Student s = me.getKey();
            String ss = me.getValue();
            System.out.println(ss+","+s.getName()+","+s.getAge());
        }
    }
}
//学生类
public class Student{
    private String name;
    private int age;

    public Student(){}
    public Student(String name,int age){
        this.name = name;
        this.age = age;
    }

    public void setName(String name){
        this.name = name;
    }
    public String getName(){
        return name;
    }

    public void setAge(int age){
        this.age = age;
    }
    public int getAge(){
        return age;
    }
}

        6、集合嵌套

        6.1集合嵌套之ArrayList嵌套HashMap

import java.util.*;

public class work11{
    public static void main(String[] args){
        ArrayList<HashMap<String,String>> array = new ArrayList<>();
        HashMap<String,String> hm1 = new HashMap<>();
        hm1.put("杨过","小龙女");
        hm1.put("郭靖","黄蓉");
        array.add(hm1);

        HashMap<String,String> hm2 = new HashMap<>();
        hm2.put("孙策","大乔");
        hm2.put("周瑜","小乔");
        array.add(hm2);

        HashMap<String,String> hm3 = new HashMap<>();
        hm3.put("李白","王昭君");
        hm3.put("干将","莫邪");
        array.add(hm3);

        for(HashMap<String,String> me:array){
            Set<String> set = me.keySet();
            for(String s:set){
                String ss = me.get(s);
                System.out.println(ss+","+s);
            }
            System.out.println("----------");
        }
        System.out.println("遍历的另一种方法:");
        for(HashMap<String,String> me:array){
            Set<Map.Entry<String,String>> entrySet = me.entrySet();
            for(Map.Entry<String,String> mo:entrySet){
                String s = mo.getKey();
                String ss = mo.getValue();
                System.out.println(s+","+ss);
            }
            System.out.println("----------");
        }
    }
}

        结果: 

 

 

        6.2集合嵌套之HashMap嵌套ArrayList

import java.util.*;

public class work {
    public static void main(String[] args){
        HashMap<String,ArrayList<String>> map = new HashMap<>();

        ArrayList<String> array1 = new ArrayList<>();
        array1.add("橙留香");
        array1.add("菠萝吹雪");
        map.put("果宝特攻",array1);

        ArrayList<String> array2 = new ArrayList<>();
        array2.add("杨过");
        array2.add("小龙女");
        map.put("神雕侠侣",array2);

        Set<Map.Entry<String,ArrayList<String>>> entrySet = map.entrySet();
        for(Map.Entry<String,ArrayList<String>> me:entrySet){
            String s = me.getKey();
            ArrayList<String> list = me.getValue();
            System.out.println(s);
            for(String ss:list){
                System.out.println("\t" + ss);
            }
        }
        System.out.println("以下是另一种方法:");
        Set<String> set = map.keySet();
        for(String s:set){
            ArrayList<String> list = map.get(s);
            System.out.println(s);
            for(String ss:list){
                System.out.println("\t" + ss);
            }
        }
    }
}

        结果: 

 

 

        7、统计字符串每个字符出现的次数

import java.util.*;

public class work {
    public static void main(String[] args){
        //从键盘录入一个字符串
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入字符串");
        String line = sc.nextLine();
        //创建HashMap集合
       HashMap<Character,Integer> hm = new HashMap<>();

        //如果要按键的顺序打印在控制面板上,使用TreeMap
        //TreeMap<Character,Integer> hm = new TreeMap<>();

        //遍历字符串,得到没一个字符
        for(int i=0;i<line.length();i++){
            char c = line.charAt(i);
            //用字符键来寻找对应的值
            Integer x = hm.get(c);
            //如果返回null,说明该字符在集合中不存在,将该字符作为键,1作为值存储
            if(x == null){
                hm.put(c,1);
            //返回的不是null,说明该字符已经存在,将该字符对应的值加1在进行存储
            }else {
                x++;
                hm.put(c,x);
            }
        }
        //创建一个StringBuilder对象,按要求进行拼接
        StringBuilder sb = new StringBuilder();
        //遍历HashMap集合
        Set<Character> set = hm.keySet();
        for(Character y:set){
            Integer i = hm.get(y);
            //按要求拼接
            sb.append(y).append("(").append(i).append(")");
        }
        String ss = sb.toString();
        System.out.println(ss);
    }
}

        结果:

         8、Collections的概述和使用

import java.util.*;

public class work{
    public static void main(String[] args){
        ArrayList<String> arrayList = new ArrayList<>();
        arrayList.add("风清扬");
        arrayList.add("林青霞");
        arrayList.add("橙留香");
        arrayList.add("菠萝吹雪");

        //sort方法排序
        Collections.sort(arrayList);
        System.out.println(arrayList);

        //reverse方法倒叙
        Collections.reverse(arrayList);
        System.out.println(arrayList);

        //shuffle方法随机排序
        Collections.shuffle(arrayList);
        System.out.println(arrayList);

    }
}

         结果:

         9、用ArrayList集合存储学生并遍历

//测试类
import java.util.*;

public class work{
    public static void main(String[] args){
        ArrayList<Student> list = new ArrayList<Student>();
        list.add(new Student("林青霞",30));
        list.add(new Student("风清扬",33));
        list.add(new Student("橙留香",10));
        Collections.sort(list, new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                int num1 = o1.getAge() - o2.getAge();
                int num2 = num1 == 0? o1.getName().compareTo(o2.getName()):num1;
                return num2;
            }
        });
        for(Student s:list){
            System.out.println(s.getName()+","+s.getAge());
        }
    }
}
//学生类
public class Student {
    private String name;
    private int age;

    public Student() {
    }

    public Student(String name,int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

        结果:

 

 

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