Java collections (seven), Map collection HashMap (common) method

 

 

Stored value of the HashMap

import java.util.*;

public class test{
    public static void main(String[] args) {
        HashMap<Integer, String> map = new HashMap<>();
        map.put(1,"leslie");
        map.put(1,"Jeo");
        map.put(2,"Sezzy");
        map.put(3,"Pit");
        System.out.println(map);
    }
}

Note: add a duplicate key will be added to cover the latest

 

HashMap values

import java.util.*;

public class test{
    public static void main(String[] args) {
        HashMap<Integer, String> map = new HashMap<>();
        map.put(1,"leslie");
        map.put(2,"Sezzy");
        map.put(3,"Pit");
        System.out.println(map.get(3));
        System.out.println(map.get("Sezzy"));
    }
}

 

Blank determination HashMap

import java.util.*;

public class test{
    public static void main(String[] args) {
        HashMap<Integer, String> map = new HashMap<>();
        System.out.println(map.isEmpty());
        map.put(1,"leslie");
        map.put(2,"Sezzy");
        map.put(3,"Pit");
        System.out.println(map.isEmpty());
    }
}

 

Determining whether the key containing HashMap

import java.util.*;

public class test{
    public static void main(String[] args) {
        HashMap<Integer, String> map = new HashMap<>();
        map.put(1,"leslie");
        map.put(2,"Sezzy");
        map.put(3,"Pit");
        System.out.println(map.containsKey(4));
        System.out.println(map.containsKey(2));
    }
}

 

 Determining whether the value contained HashMap

import java.util.*;

public class test{
    public static void main(String[] args) {
        HashMap<Integer, String> map = new HashMap<>();
        map.put(1,"leslie");
        map.put(2,"Sezzy");
        map.put(3,"Pit");
        System.out.println(map.containsValue("wang"));
        System.out.println(map.containsValue("Sezzy"));
    }
}

 

HashMap delete this value at key

import java.util.*;

public class test{
    public static void main(String[] args) {
        HashMap<Integer, String> map = new HashMap<>();
        map.put(1,"leslie");
        map.put(2,"Sezzy");
        map.put(3,"Pit");
        System.out.println(map.remove(2));
        System.out.println(map);
    }
}

 

HashMap show the value of all values

import java.util.*;

public class test{
    public static void main(String[] args) {
        HashMap<Integer, String> map = new HashMap<>();
        map.put(1,"leslie");
        map.put(2,"Sezzy");
        map.put(3,"Pit");
        System.out.println(map.values());
        System.out.println(map);
    }
}

 

The number of elements HashMap

import java.util.*;

public class test{
    public static void main(String[] args) {
        HashMap<Integer, String> map = new HashMap<>();
        System.out.println(map.size());
        map.put(1,"leslie");
        map.put(2,"Sezzy");
        map.put(3,"Pit");
        System.out.println(map.size());
    }
}

 

Remove all of the key HashMap

import java.util.*;

public class test{
    public static void main(String[] args) {
        HashMap<Integer, String> map = new HashMap<>();
        System.out.println(map.keySet());
        map.put(1,"leslie");
        map.put(2,"Sezzy");
        System.out.println(map.keySet());
        map.put(3,"Pit");
        System.out.println(map.keySet());
        System.out.println(map);
    }
}

 

HashMap replace the key value

import java.util.*;

public class test{
    public static void main(String[] args) {
        HashMap<Integer, String> map = new HashMap<>();
        map.put(1,"leslie");
        map.put(2,"Sezzy");
        map.put(3,"Pit");
        System.out.println(map);
        System.out.println(map.replace(3, "Jack"));
        System.out.println(map);
    }
}

 

Clear this HashMap

import java.util.*;

public class test{
    public static void main(String[] args) {
        HashMap<Integer, String> map = new HashMap<>();
        map.put(1,"leslie");
        map.put(2,"Sezzy");
        map.put(3,"Pit");
        System.out.println(map);
        map.clear();
        System.out.println(map);
    }
}

 

HashMap clone

import java.util.*;

public class test{
    public static void main(String[] args) {
        HashMap<Integer, String> map = new HashMap<>();
        map.put(1,"leslie");
        map.put(2,"Sezzy");
        map.put(3,"Pit");
        System.out.println(map.clone());
        Object clone = map.clone();
        System.out.println(clone);
    }
}

 

If the current  Map key does not exist  key  or the  key  associated value  null, then the execution  put(key, value); otherwise, it will not perform the  put operation: (java8 new method)

import java.util.*;

public class test{
    public static void main(String[] args) {
        HashMap<Integer, String> map = new HashMap<>();
        map.put(1,"leslie");
        map.put(2,"Sezzy");
        map.put(3,"Pit");
        System.out.println(maps);
        System.out.println(map.putIfAbsent(1, "wang"));
        System.out.println(map.putIfAbsent(4, "Lee"));
        System.out.println(map);
    }
}

 

If the current  Map is the value when the value is otherwise xx xx xx: (java8 new method) compute method is available to update  key  associated  value  , the new value of the case depends on the value of old 

import java.util.*;

public class test{
    public static void main(String[] args) {
        HashMap<Integer, String> map = new HashMap<>();
        map.put(1,"leslie");
        map.put(2,"Sezzy");
        map.put(3,"Pit");
        System.out.println(map);
        map.compute(2, (k, v) -> v == null ? "Suzan" : "Faker");
        System.out.println(map);
    }
}