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Javase learning notes 19: Collection (5)

Group review

What is the main content of the collection ?

  1. The creation of each collection object (new)
  2. Add elements to the collection
  3. Take the element from the collection
  4. Ergodic set

The main set class :

  1. ArrayList
  2. LinkedList
  3. HashSet(HashSet Of key、 Stored in HashMap aggregate key The elements of need to be rewritten at the same time hashCode + equals Method )
  4. TreeSet
  5. HashMap
  6. Properties
  7. TreeMap

review List What the assembly needs to master

package se3.review;

import java.util.ArrayList;
import java.util.Iterator;

/** Need to master the content :
 * 1.  The creation of each collection object (new)
 * 2.  Add elements to the collection 
 * 3.  Take the element from the collection 
 * 4.  Ergodic set 
 */
public class ArrayListTest {
    public static void main(String[] args) {
        // Create a collection object 
        ArrayList<String> list = new ArrayList<>();
        // Additive elements 
        list.add(" Zhang San ");
        list.add(" Li Si ");
        list.add(" Wang Wu ");
        // Take an element out of a collection .(List Sets have subscripts )
        String firstElt = list.get(0);
        System.out.println(firstElt);// Zhang San 
        // Traverse : Subscript mode 
        for (int i = 0; i < list.size(); i++) {
            String elt = list.get(i);
            System.out.print(elt + " ");
        }
        System.out.println();
        
        // Traverse : Iterator mode ( General purpose , be-all Collection Can be used )
        Iterator<String> it = list.iterator();
        while (it.hasNext()){
            System.out.print(it.next() + " ");
        }
        System.out.println();
        
        // Traverse :foreach The way 
        for (String s : list){
            System.out.print(s + " ");
        }
        /**
         *  The above three ways of traversing the output are the same 
         *  Zhang San   Li Si   Wang Wu 
         */
    }
}

Be careful :LinkedList The content is the same as above (ArrayList Change it to LinkedList that will do )

review HashSet What needs to be mastered

package se3.review;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Objects;
import java.util.Set;

/** Need to master the content :
 * 1.  The creation of each collection object (new)
 * 2.  Add elements to the collection 
 * 3.  Take the element from the collection 
 * 4.  Ergodic set 
 * 5.  test HashSet Set characteristics : Disorder cannot be repeated 
 */
public class HashSetTest {
    public static void main(String[] args) {
        // Create a collection object 
        HashSet<String> set = new HashSet<>();
        // Additive elements 
        set.add("abc");
        set.add("def");
        set.add("king");
        //set Set elements cannot be indexed ( No subscript )
        // Traverse : Iterator mode 
        Iterator<String> it = set.iterator();
        while (it.hasNext()){
            System.out.print(it.next() + " ");
        }
        System.out.println();

        //foreach The way 
        for (String s : set){
            System.out.print(s + " ");
        }
        System.out.println();

        // test HashSet Set characteristics 
        set.add("king");
        set.add("king");
        set.add("king");
        System.out.println(set.size());//3( Back 3 individual King They didn't add in )
        set.add("1");
        set.add("10");
        set.add("2");
        for (String s : set){
            System.out.print(s + " ");
        }//1 2 abc def king 10
        System.out.println();

        // Create set , Storage Student data 
        Set<Student> students = new HashSet<>();
        Student s1 = new Student(1," Zhang San ");
        Student s2 = new Student(2," Li Si ");
        Student s3 = new Student(1," Zhang San ");
        students.add(s1);
        students.add(s2);
        students.add(s3);
        System.out.println(students.size());//2
        // Traverse 
        for (Student stu : students){
            System.out.println(stu);
        }
        /**
         *  Student { Student number =2,  full name =' Li Si '}
         *  Student { Student number =1,  full name =' Zhang San '}
         */
    }
}
class Student{
    int no;
    String name;

    public Student() {
    }

    public Student(int no, String name) {
        this.no = no;
        this.name = name;
    }

    @Override
    public String toString() {
        return " Student {" +
                " Student number =" + no +
                ",  full name ='" + name + '\'' +
                '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Student student = (Student) o;
        return no == student.no &&
                Objects.equals(name, student.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(no, name);
    }
}

review TreeSet What needs to be mastered

package se3.review;

import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeSet;

/** Need to master the content :
 * 1.  The creation of each collection object (new)
 * 2.  Add elements to the collection 
 * 3.  Take the element from the collection 
 * 4.  Ergodic set 
 * 5.  test TreeSet aggregate :TreeSet The elements in a collection are sortable , Non repeatable 
 * 6.  test TreeSet The type stored in the collection is custom 
 * 7.  Test implementation Comparable How to interface 
 * 8.  Test implementation Compa How to interface ( And the way to anonymous inner classes )
 */
public class TreeSetTest {
    public static void main(String[] args) {
        // Create set 
        TreeSet<Integer> ts = new TreeSet<>();
        // Additive elements 
        ts.add(1);
        ts.add(100);
        ts.add(10);
        ts.add(10);
        ts.add(10);
        ts.add(10);
        ts.add(0);
        // Traverse ( iterator )
        Iterator<Integer> it = ts.iterator();
        while (it.hasNext()){
            System.out.print(it.next() + " ");
        }//0 1 10 100
        System.out.println();
        // Traverse (foreach)
        for (Integer i : ts){
            System.out.print(i + " ");
        }//0 1 10 100
        System.out.println();

        //TreeSet Collection to store custom types ( The first way )
        TreeSet<A> atree = new TreeSet<>();
        atree.add(new A(100));
        atree.add(new A(200));
        atree.add(new A(500));
        atree.add(new A(400));
        atree.add(new A(300));
        atree.add(new A(1000));
        // Traverse 
        for (A a : atree){
            System.out.print(a + " ");
        }//A{i=100} A{i=200} A{i=300} A{i=400} A{i=500} A{i=1000}
        System.out.println();

        //TreeSet Collection to store custom types ( The second way , The comparator )
        TreeSet<B> btree = new TreeSet<>(new BComparator());
        btree.add(new B(500));
        btree.add(new B(100));
        btree.add(new B(200));
        btree.add(new B(600));
        btree.add(new B(300));
        btree.add(new B(50));
        for (B b : btree){
            System.out.print(b + " ");
        }//B{i=50} B{i=100} B{i=200} B{i=300} B{i=500} B{i=600}
        System.out.println();

        // The anonymous inner class way of comparator 
        TreeSet<C> ctree = new TreeSet<>(new Comparator<C>() {
            @Override
            public int compare(C o1, C o2) {
                return o1.i - o2.i;
            }
        });
        ctree.add(new C(700));
        ctree.add(new C(800));
        ctree.add(new C(200));
        ctree.add(new C(600));
        ctree.add(new C(900));
        ctree.add(new C(90));
        for (C c : ctree){
            System.out.print(c + " ");
        }//C{i=90} C{i=200} C{i=600} C{i=700} C{i=800} C{i=900} 
    }
}// The first way : Realization Comparable Interface 
class A implements Comparable<A>{
    int i;

    public A(int i) {
        this.i = i;
    }

    @Override
    public String toString() {
        return "A{" +
                "i=" + i +
                '}';
    }

    @Override
    public int compareTo(A o) {
        return this.i - o.i;
    }
}
// The second way : Delivery comparator 
class B {
    int i;

    public B(int i) {
        this.i = i;
    }

    @Override
    public String toString() {
        return "B{" +
                "i=" + i +
                '}';
    }
}
// The comparator 
class BComparator implements Comparator<B>{

    @Override
    public int compare(B o1, B o2) {
        return o1.i - o2.i;
    }
}

class C {
    int i;

    public C(int i) {
        this.i = i;
    }

    @Override
    public String toString() {
        return "C{" +
                "i=" + i +
                '}';
    }
}

Be careful :TreeMap The content is the same as above

review HashMap What needs to be mastered

package se3.review;

import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;
import java.util.Set;

/** Need to master the content :
 * 1.  The creation of each collection object (new)
 * 2.  Add elements to the collection 
 * 3.  Take the element from the collection 
 * 4.  Ergodic set 
 */
public class HashMapTest {
    public static void main(String[] args) {
        // Create set 
        Map<Integer,String> map = new HashMap<>();
        // Additive elements 
        map.put(1," Zhang San ");
        map.put(9," Li San ");
        map.put(10," Wang Wu ");
        map.put(2," Zhao Liu ");
        map.put(2," APO ");//key Can be repeated ,value Will be covered 
        // Get the number of elements 
        System.out.println(map.size());//4
        // take key yes 2 The elements of 
        System.out.println(map.get(2));// APO 
        // Traverse Map Assembly is important , You have to be able to 
        // The first way : Get all of it first key, Traverse key When , adopt key obtain value
        Set<Integer> keys = map.keySet();
        for (Integer key : keys){
            System.out.println(key + "=" + map.get(key));
        }
        /**
         * 1= Zhang San 
         * 2= APO 
         * 9= Li San 
         * 10= Wang Wu 
         */
        System.out.println("##################################");
        // The second way : take Map Set to Set aggregate ,Set Each element in the set is Node
        // This Node Node has key and value
        Set<Map.Entry<Integer,String>> nodes = map.entrySet();
        for (Map.Entry<Integer,String> node : nodes){
            System.out.println(node.getKey() + "=" + node.getValue());
        }/**
         * 1= Zhang San 
         * 2= APO 
         * 9= Li San 
         * 10= Wang Wu 
         */
    }
}

review Properties What needs to be mastered

package se3.review;

import java.util.Properties;
/** Need to master the content :
 * 1.  The creation of each collection object (new)
 * 2.  Add elements to the collection 
 * 3.  Take the element from the collection 
 */
public class PropertiesTest {
    public static void main(String[] args) {
        // Create objects 
        Properties pro = new Properties();
        // save 
        pro.setProperty("username"," Zhang San ");
        pro.setProperty("password","123");
        // take 
        String username = pro.getProperty("username");
        String password = pro.getProperty("password");
        System.out.println(username);// Zhang San 
        System.out.println(password);//123
    }
}

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