Common Operations on the List set in Java, javalist set

Common Operations on the List set in Java, javalist set

Directory:

 

Note: the code in the content is correlated.

1. Add, retrieve, and delete elements in the list;

The add method is :. add (e); The Obtaining method is :. get (index); the deletion method is :. remove (index); Delete by index ;. remove (Object o); Delete according to the element content;

List <String> person = new ArrayList <> (); person. add ("jackie"); // The index is 0 //. add (e) person. add ("peter"); // The index is 1person. add ("annie"); // The index is 2person. add ("martin"); // The index is 3person. add ("marry"); // The index is 4person. remove (3 );//. remove (index) person. remove ("marry ");//. remove (Object o) String per = ""; per = person. get (1); System. out. println (per );////. get (index) for (int I = 0; I <person. size (); I ++) {System. out. println (person. get (I ));//. get (index )}

 

2. Whether the list contains an element;

Method:. contains (Object o); returns true or false

List <String> fruits = new ArrayList <> (); fruits. add ("apple"); fruits. add ("banana"); fruits. add ("Peach"); // for Loop listfor (int I = 0; I <fruits. size (); I ++) {System. out. println (fruits. get (I);} String appleString = "apple"; // true or falseSystem. out. println ("Does fruits contain Apple:" + fruits. contains (appleString); if (fruits. contains (appleString) {System. out. println ("I like Apple");} else {System. out. println ("I'm not happy ");}

 

3. Change (replace) the element values in the list based on the index );

Note the differences between. set (index, element); and. add (index, element;

String a = "White Dragon Horse", B = "Sha Monk", c = "ba Jie", d = "Tang Seng", e = "Wukong "; list <String> people = new ArrayList <> (); people. add (a); people. add (B); people. add (c); people. set (0, d );//. set (index, element); // place d Tang Seng in the list to 0 and replace a White Dragon Horse people. add (1, e );//. add (index, element); // put e Wukong to the position where the index is 1 in the list, and the B Sha monk at the original position moves one after. // enhance the for loop traversal listfor (String str: people) {System. out. println (str );}

 

4. View (judge) the index of the element in the list;　

Note:. indexOf (); and lastIndexOf () are different;

List <String> names = new ArrayList <> (); names. add ("Liu Bei"); // The index is 0 names. add ("Guan Yu"); // The index is 1 names. add ("Zhang Fei"); // The index is 2names. add ("Liu Bei"); // The index is 3names. add ("Zhang Fei"); // The index is 4System. out. println (names. indexOf ("Liu Bei"); System. out. println (names. lastIndexOf ("Liu Bei"); System. out. println (names. indexOf ("Zhang Fei"); System. out. println (names. lastIndexOf ("Zhang Fei "));

 

5. Determine the index position of an element;

If (names. indexOf ("Liu Bei") = 0) {System. out. println ("Liu Bei here");} else if (names. lastIndexOf ("Liu Bei") = 3) {System. out. println ("Liu Bei there");} else {System. out. println ("Where is Liu Bei? ");}

 

6. Use the index position in the list to re-generate a new list (truncation set );

Method:. subList (fromIndex, toIndex);. size (); this method obtains the sum of the number of elements in the list.

List <String> phone = new ArrayList <> (); phone. add ("Samsung"); // The index is 0 phone. add ("apple"); // The index is 1 phone. add ("Hammer"); // The index is 2phone. add ("Huawei"); // The index is 3phone. add ("Xiaomi"); // The index is 4 // the original list is traversed for (String pho: phone) {System. out. println (pho);} // generate a new listphone = phone. subList (1, 4 );//. subList (fromIndex, toIndex) // use the object of Index 1-4 to generate a new list, but it does not contain the element with index 4, 4-1 = 3for (int I = 0; I <phone. size (); I ++) {// phone. size () This method returns the number of elements in the list and System. out. println ("the new list contains" + phone. get (I ));}

 

7. Compare all elements in the two lists;

// The equals method of two equal objects must be true, but the two objects with the same hashcode are not necessarily equal objects.

// 1.
If (person. equals (fruits) {System. out. println ("all elements in the two lists are the same");} else {System. out. println ("all elements in two lists are different");} // 2.if (person. hashCode () = fruits. hashCode () {System. out. println ("we are the same");} else {System. out. println ("we are different ");}

 

8. Check whether the list is empty;

// If it is null, true is returned. If it is not null, false is returned.

If (person. isEmpty () {System. out. println ("null");} else {System. out. println ("not empty ");}

 

9. Return the Iterator set object;

System. out. println ("Returned Iterator collection object:" + person. iterator ());

 

1 + 0. Convert the set to a string;

String liString = ""; liString = person. toString (); System. out. println ("convert the set to String:" + liString );

 

11. Convert the set into an array;

System. out. println ("convert the set to an array:" + person. toArray ());

 

12. Set type conversion;

// 1. default type List <Object> listsStrings = new ArrayList <> (); for (int I = 0; I <person. size (); I ++) {listsStrings. add (person. get (I);} // 2. list <StringBuffer> lst = new ArrayList <> (); for (String string: person) {lst. add (StringBuffer (string ));}

 

Complete code:

Package MyTest01; import java. util. arrayList; import java. util. list; public class ListTest01 {public static void main (String [] args) {// Add, retrieve, and delete the element list <String> person = new ArrayList <> (); person. add ("jackie"); // The index is 0 //. add (e) person. add ("peter"); // The index is 1person. add ("annie"); // The index is 2person. add ("martin"); // The index is 3person. add ("marry"); // The index is 4person. remove (3 );//. remove (index) person. remove ("marry ");//. remove (Object o) String per = ""; per = person. get (1); System. out. println (per );////. get (index) for (int I = 0; I <person. size (); I ++) {System. out. println (person. get (I ));//. get (index)} // whether the list contains a List of elements <String> fruits = new ArrayList <> (); fruits. add ("apple"); fruits. add ("banana"); fruits. add ("Peach"); // for Loop listfor (int I = 0; I <fruits. size (); I ++) {System. out. println (fruits. get (I);} String appleString = "apple"; // true or falseSystem. Out. println ("Does fruits contain Apple:" + fruits. contains (appleString); if (fruits. contains (appleString) {System. out. println ("I like Apple");} else {System. out. println ("I'm not happy");} // change (replace) the element value in the list based on the index String a = "White Dragon Horse", B = "Sha Monk ", c = "", d = "", e = "Wukong"; List <String> people = new ArrayList <> (); people. add (a); people. add (B); people. add (c); people. set (0, d );//. set (index, element) // place d Tang Seng in the list to 0 and replace a White Dragon Horse people. add (1, e );//. add (I Ndex, element); // put e Wukong to the position where the index is 1 in the list, and the B-sand monk at the original position moves one after. // enhance the for loop traversal listfor (String str: people) {System. out. println (str);} // The index list of the (judgement) element in the List <String> names = new ArrayList <> (); names. add ("Liu Bei"); // The index is 0 names. add ("Guan Yu"); // The index is 1 names. add ("Zhang Fei"); // The index is 2names. add ("Liu Bei"); // The index is 3names. add ("Zhang Fei"); // The index is 4System. out. println (names. indexOf ("Liu Bei"); System. out. println (names. lastIndexOf ("Liu Bei"); System. out. println (names. indexOf ("Zhang Fei ")); System. out. println (names. lastIndexOf ("Zhang Fei"); // determine if (names. indexOf ("Liu Bei") = 0) {System. out. println ("Liu Bei here");} else if (names. lastIndexOf ("Liu Bei") = 3) {System. out. println ("Liu Bei there");} else {System. out. println ("Where is Liu Bei? ");} // Use the index position in the list to regenerate a new list (truncated set) List <String> phone = new ArrayList <> (); phone. add ("Samsung"); // The index is 0 phone. add ("apple"); // The index is 1 phone. add ("Hammer"); // The index is 2phone. add ("Huawei"); // The index is 3phone. add ("Xiaomi"); // The index is 4 // the original list is traversed for (String pho: phone) {System. out. println (pho);} // generate a new listphone = phone. subList (1, 4 );//. subList (fromIndex, toIndex) // use the object of Index 1-4 to generate a new list, but it does not contain the element with index 4, 4-1 = 3for (int I = 0; I <phone. size (); I ++) {// phone. size () This method returns the number of elements in the list and System. out. println ("the new list contains" + phone. get (I);} // compare all the elements in the two lists. // The equals method of the two equal objects must be true, but the two objects with the same hashcode are not necessarily the same object if (person. equals (fruits) {System. out. println ("all elements in the two lists are the same");} else {System. out. println ("all elements in two lists are different");} if (person. hashCode () = fruits. hashCode () {System. out. println ("we are the same");} else {System. out. println ("we are different");} // determines whether the list is empty. // if it is null, true is returned. If it is not null, falseif (person. isEmpty () {System. out. println ("null");} else {System. out. println ("not empty");} // returns the Iterator set object System. out. println ("Returned Iterator set object:" + person. iterator (); // convert the set to String liString = ""; liString = person. toString (); System. out. println ("convert a set to a string:" + liString); // convert a set to an array. The default type is System. out. println ("convert a set to an array:" + person. toArray (); // convert the set to a specified type (friendly processing) // 1. default type List <Object> listsStrings = new ArrayList <> (); for (int I = 0; I <person. size (); I ++) {listsStrings. add (person. get (I);} // 2. list <StringBuffer> lst = new ArrayList <> (); for (String string: person) {lst. add (StringBuffer (string) ;}} private static StringBuffer (String string) {return null ;}}