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1. Nextint (), nextline (), Next () the difference between the three:

1. Nextine (): Input value with focus, nextline (): newline input, focus change, Next (): No newline input, focus unchanged.

2. If Nextint () is placed first, the following two scenarios need to be considered:

   (1) Scanner s = new Scanner (system.in);

   System.out.println ("Please enter user name:");

   int a = S.nextint ();//has focus set in the same row;

   System.out.println ("Please enter password:");

   String B = s.nextline ();//Force line break, which loses focus, so cannot enter

   1. 
      

3. (2) Scanner s = new Scanner (system.in);

4. 
   

System.out.println ("Please enter user name:");

int A=s.nextint (); Has the focus set in the same row;

System.out.println ("Please enter password:");

String B = S.next (); This is the focus of the same line, so it can be entered;

Two common methods for 2.MAP interfaces:

KeySet (): The return type is a set interface, and the key value is placed inside the set container;

VALUES (): The return type is the collection interface, and the value is placed inside the collection container;

3.Arrays: Sort or search for an array

Common methods:

Sort (array type); From small to large sort;

ToString (array type); Returns a string type;

4.Collections: Sorting or searching for a container

Common methods:

Sort (list list); From small to large sort;

Shuffle (list list); Replaces the specified list with a default random source.

Reverse (list list); Reverses the elements in the container;

5. Enhanced content for generics:

Definition: Refers to the complexity of the type into uniqueness. Must be a reference type or a custom type.

There are four common methods:

(1) You can use < T > to represent any type, as long as the main method gives it a type;

(2) generic type can inherit:< T extends Collection, at this time in the method after the given type is immutable;

(3) wildcard character:<? Extends Collection, at this time in the main method can be given any one of the super-interface implementation class;

(4) How to use generics: You must precede the return value type with < T >; such as: public < T > void f (t x) {}

Commonly called methods: System.out.println (X.getclass (). GetName ());

Note: To understand the object

After-school exercises:

1. Known: There is a two-dimensional array: int[][] a={{5,4},{3,2},{9,7}};
   

   To sort, the result is: 2,3,4,5,7,9;

   Knowledge points used: List interface, Collections class, two-dimensional array traversal;

Code:

public class Paixu {

public static void Main (string[] args) {

Int[][] a={{5,4},{3,2},{9,7}};

ArrayList ArrayList = new ArrayList ();

Traverse a two-dimensional array and put the results into the container ArrayList

For (int[] b:a) {

for (int i:b) {

Arraylist.add (i);

}

}

Collections.sort (arrayList); Sort the elements in ArrayList in ascending order

Iterate through the sorted ArrayList and output the elements individually

for (int j:arraylist) {

System.out.print (j);

if (J==arraylist.get (Arraylist.size ()-1)) {

Break

}

System.out.print (",");

}

}

}

2.

HashMap make an alternative, {1 = "xiaoming", 2 = "Small East", 3 = "Little West"}

"Xiao Ming" instead of "Xiao Red", and then the value in this, take out the reverse after, the West small, east small, red small

Code:

public class Replacer {

public static void Main (string[] args) {

hashmap<integer,string> HashMap = new hashmap<integer,string> ();

Hashmap.put (1, "xiaoming");

Hashmap.put (2, "Little East");

Hashmap.put (3, "Xiao Xi");

Hashmap.put (1, "Little Red"); To replace Xiao Ming as "Xiao Hong"

collection<string> value = Hashmap.values (); Remove value values

linkedlist<string> list = new linkedlist<string> ();

for (String Str:value) {

List.add (str);

}

Collections.reverse (Stringbuff);

StringBuffer stringbuff = null;

int i==0;

for (String str1:list) {

Stringbuff = new StringBuffer (STR1);

Stringbuff.reverse ();

System.out.print (Stringbuff);

if (I==list.size ()-1) {//through I to eliminate the end of the output of an extra ","

Break

}

System.out.print (",");

i++;

}

}

}

This article is from the "Kun" blog, please be sure to keep this source http://linyingkun.blog.51cto.com/2393912/1575923

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