Common methods of ArrayList
Step 1: add
add can be used in two ways:
The first is to add the object directly, adding the object at the end
heros.add(new Hero("hero " + i));The second is to add objects at the specified location
heros.add(3, specialHero);
package collection;
import java.util.ArrayList;
import charactor.Hero;
public class TestCollection {
public static void main(String[] args) {
ArrayList heros = new ArrayList();
// Add 5 objects to ArrayList
for (int i = 0; i < 5; i++) {
heros.add(new Hero("hero " + i));
}
System.out.println(heros);
// Add object at specified location
Hero specialHero = new Hero("special hero");
heros.add(3, specialHero);
System.out.println(heros.toString());
}
}
package charactor;
public class Hero {
public String name;
public float hp;
public int damage;
public Hero() {
}
// Add a construction method to initialize name
public Hero(String name) {
this.name = name;
}
// Override toString method
public String toString() {
return name;
}
}Step 2: judge whether it exists
Determine whether an object is in the container through the methods contains
Judgment criteria: whether the object is the same, not whether the name is the same
package collection;
import java.util.ArrayList;
import charactor.Hero;
public class TestCollection {
public static void main(String[] args) {
ArrayList heros = new ArrayList();
// Initialize 5 objects
for (int i = 0; i < 5; i++) {
heros.add(new Hero("hero " + i));
}
Hero specialHero = new Hero("special hero");
heros.add(specialHero);
System.out.println(heros);
// Determine whether an object is in a container
// Judgment criteria: whether the object is the same, not whether the name is the same
System.out.print("Although a new object's name is also called hero 1，however contains The return is:");
System.out.println(heros.contains(new Hero("hero 1")));
System.out.print("But on specialHero Judgement, contains The return is:");
System.out.println(heros.contains(specialHero));
}
}Step 3: get the object at the specified location
get the object at the specified location. If the input subscript is out of range, an error will also be reported 
package collection;
import java.util.ArrayList;
import charactor.Hero;
public class TestCollection {
public static void main(String[] args) {
ArrayList heros = new ArrayList();
// Initialize 5 objects
for (int i = 0; i < 5; i++) {
heros.add(new Hero("hero " + i));
}
Hero specialHero = new Hero("special hero");
heros.add(specialHero);
//Gets the object at the specified location
System.out.println(heros.get(5));
//If it goes beyond the scope, it will still report an error
System.out.println(heros.get(6));
}
}Step 4: get the location of the object
indexOf is used to determine the position of an object in the ArrayList
As with contains, the criterion is whether the object is the same, not whether the name value of the object is the same
package collection;
import java.util.ArrayList;
import charactor.Hero;
public class TestCollection {
public static void main(String[] args) {
ArrayList heros = new ArrayList();
// Initialize 5 objects
for (int i = 0; i < 5; i++) {
heros.add(new Hero("hero " + i));
}
Hero specialHero = new Hero("special hero");
heros.add(specialHero);
System.out.println(heros);
System.out.println("specialHero Location:"+heros.indexOf(specialHero));
System.out.println("New hero, but the name is\"hero 1\"Location:"+heros.indexOf(new Hero("hero 1")));
}
}Step 5: delete
Remove is used to remove objects from the ArrayList
remove can delete the elements of ArrayList according to the subscript
heros.remove(2);
It can also be deleted according to the object
heros.remove(specialHero);
package collection;
import java.util.ArrayList;
import charactor.Hero;
public class TestCollection {
public static void main(String[] args) {
ArrayList heros = new ArrayList();
// Initialize 5 objects
for (int i = 0; i < 5; i++) {
heros.add(new Hero("hero " + i));
}
Hero specialHero = new Hero("special hero");
heros.add(specialHero);
System.out.println(heros);
heros.remove(2);
System.out.println("Delete object with subscript 2");
System.out.println(heros);
System.out.println("delete special hero");
heros.remove(specialHero);
System.out.println(heros);
}
}Step 6: replace
set is used to replace the element at the specified location
package collection;
import java.util.ArrayList;
import charactor.Hero;
public class TestCollection {
public static void main(String[] args) {
ArrayList heros = new ArrayList();
// Initialize 5 objects
for (int i = 0; i < 5; i++) {
heros.add(new Hero("hero " + i));
}
Hero specialHero = new Hero("special hero");
heros.add(specialHero);
System.out.println(heros);
System.out.println("Replace element with subscript 5 with\"hero 5\"");
heros.set(5, new Hero("hero 5"));
System.out.println(heros);
}
}Step 7: get the size
Size to get the size of the ArrayList
package collection;
import java.util.ArrayList;
import charactor.Hero;
public class TestCollection {
public static void main(String[] args) {
ArrayList heros = new ArrayList();
// Initialize 5 objects
for (int i = 0; i < 5; i++) {
heros.add(new Hero("hero " + i));
}
Hero specialHero = new Hero("special hero");
heros.add(specialHero);
System.out.println(heros);
System.out.println("Obtain ArrayList Size:");
System.out.println(heros.size());
}
}Step 8: convert to array
toArray can convert an ArrayList object to an array.
It should be noted that if you want to convert to a Hero array, you need to pass an Object of Hero array type to toArray(), so that the toArray method can know which type of array you want to convert, otherwise you can only convert to an Object array
package collection;
import java.util.ArrayList;
import charactor.Hero;
public class TestCollection {
public static void main(String[] args) {
ArrayList heros = new ArrayList();
// Initialize 5 objects
for (int i = 0; i < 5; i++) {
heros.add(new Hero("hero " + i));
}
Hero specialHero = new Hero("special hero");
heros.add(specialHero);
System.out.println(heros);
Hero hs[] = (Hero[])heros.toArray(new Hero[]{});
System.out.println("array:" +hs);
}
}Step 9: add all objects in another container
addAll adds all objects in another container
package collection;
import java.util.ArrayList;
import charactor.Hero;
public class TestCollection {
public static void main(String[] args) {
ArrayList heros = new ArrayList();
// Initialize 5 objects
for (int i = 0; i < 5; i++) {
heros.add(new Hero("hero " + i));
}
System.out.println("ArrayList heros:\t" + heros);
//Add all the elements in another container to the container
ArrayList anotherHeros = new ArrayList();
anotherHeros.add(new Hero("hero a"));
anotherHeros.add(new Hero("hero b"));
anotherHeros.add(new Hero("hero c"));
System.out.println("anotherHeros heros:\t" + anotherHeros);
heros.addAll(anotherHeros);
System.out.println("Turn the other one. ArrayList All elements of are added to the current ArrayList:");
System.out.println("ArrayList heros:\t" + heros);
}
}Step 10: empty
clear clears an ArrayList
package collection;
import java.util.ArrayList;
import charactor.Hero;
public class TestCollection {
public static void main(String[] args) {
ArrayList heros = new ArrayList();
// Initialize 5 objects
for (int i = 0; i < 5; i++) {
heros.add(new Hero("hero " + i));
}
System.out.println("ArrayList heros:\t" + heros);
System.out.println("Use clear empty");
heros.clear();
System.out.println("ArrayList heros:\t" + heros);
}
}