# How to add a new item in a arraylist when this class is defined by myself?

**URL:** <https://discourse.processing.org/t/how-to-add-a-new-item-in-a-arraylist-when-this-class-is-defined-by-myself/36944>\
**Category:** Coding Questions\
**Tags:** homework\
**Created:** [May 18, 2022, 2:00pm UTC](https://discourse.processing.org/t/how-to-add-a-new-item-in-a-arraylist-when-this-class-is-defined-by-myself/36944 "2022-05-18T14:00:40Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![Lee027](https://avatars.discourse-cdn.com/v4/letter/l/e47774/32.png) [@Lee027](https://discourse.processing.org/u/Lee027)\
**Post date:** [May 18, 2022, 2:00pm UTC](https://discourse.processing.org/t/how-to-add-a-new-item-in-a-arraylist-when-this-class-is-defined-by-myself/36944/1 "2022-05-18T14:00:40Z")

</div>

I defined a class named (drop) to represent a moving cloud with rain. And then I created an array uninitialized named (drops[]) to represent a list will increase automatically with ‘for loop’ in a table.  
But when using append to add the new drop, the feed back told me that Type mismatch, “java.lang.Object” does not match with “sketch\_220516a.drop[]”.  
Anyone helps me?  
I’m a Chinese, not very good at English, if this description isn’t clear. Here is the code:

useful part only in “draw()”

//public\_variable\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  
PImage watch, dwr;  
Table table;  
float p, w;  
int year = 2021;  
//set\_map\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  
void setup() {  
table = loadTable(“beijing.csv”, “header”);  
size(1000, 1000);  
background(255);  
PFont cityFont;  
dwr = loadImage(“dwr.png”);  
cityFont = loadFont(“Anton-Regular-32.vlw”);  
PFont numFont;  
numFont = createFont(“andalemo.ttf”, 12);  
textAlign(CENTER);

int circlenum = 6, circledist = 80;  
String city = “BeiJing\nChina”;  
pushMatrix();  
translate(width/2, height/2);

for (int i=0; i\<circlenum; i++) {  
strokeWeight(1);  
if (i==2) {  
strokeWeight(3);  
}  
noFill();  
stroke(220);  
circle(0, 0, 150+i_circledist);  
}  
strokeWeight(30);  
stroke(255);  
line(0, height/2, 0, 0);  
strokeWeight(18);  
line(0, -200, 0, 0);  
strokeWeight(1);  
stroke(220);  
fill(220);  
line(0, -203, 0, -283);  
quad(0, -282, 40, -278, 0, -290, -40, -278);  
textFont(numFont);  
for (int i=0; i\<circlenum; i++) {  
strokeWeight(2);  
if (i==2) {  
strokeWeight(3);  
}  
fill(200);  
text(str(-20+i_10)+“°C”, 0, (150+i\*circledist)/2+5);  
}  
strokeWeight(5);  
textFont(cityFont, 34);  
text(city, 0, -8);  
textFont(cityFont, 14);  
text(“RH”, 0, -70);  
text(“70”, 0, -108);  
text(“40”, 0, -148);  
text(year, 0, -300);  
triangle(-2, -195, -8, -197, -8, -193);  
String[] mon = {“Jan.”, “Feb.”, “Mar.”, “APR.”, “May.”, “Jun.”, “Jul.”, “Aug.”, “Sept.”, “Oct.”, “Nov.”, “Dec.”};  
rotate(-PI/2+0.3);

for (int i = 0; i\<12; i++) {  
translate(300, 0);  
rotate(PI/2);  
textSize(20);  
text(mon[i], 0, 0);  
rotate(-PI/2);  
translate(-300, 0);  
rotate(2\*PI/12);  
}

float t, s, at;

for (int i= 1; i\<365; i++) {  
t = table.getRow(i).getFloat(“T”);  
p = table.getRow(i).getFloat(“P”);  
s = table.getRow(i).getFloat(“S”);  
w = table.getRow(i).getFloat(“W”);  
at = table.getRow(i).getFloat(“AT”);  
year = 2021;  
//year = table.getRow(i).getInt(“y”);

```
//RH first
translate(180, 0);
strokeWeight(2);
noFill();
translate(-s/2, 0);
stroke(255-s/3);
line(0, 0, -s/2, 0);
translate(s/2, 0);
translate(-180, 0);
//temp second

strokeWeight(2);
translate(150, 0);
//colorRank
if (t>32) stroke(240, 52, 52);//hong
if (t<32) stroke(255, 149, 38);//cheng
if (t<28) stroke(255, 230, 0);//huang
if (t<25) stroke(20, 218, 51);//lv
if (t<22) stroke(175, 255, 34);//huanglv
if (t<19) stroke(10, 220, 186);//qinglv
if (t<11) stroke(10, 170, 220);//tianlan
if (t<0) stroke(34, 178, 255);//bing
if (t<-5) stroke(34, 138, 255);//lan
if (t<-10) stroke(34, 101, 255);//
if (t<-15) stroke(54, 42, 211);
if (t<-20) stroke(99, 42, 211);

line(4*at, 0, 4*t, 0);

translate(-150, 0);
rotate(2*PI/365);

```

}  
popMatrix();  
noStroke();  
pushMatrix();  
translate(width/2, height/2);  
fill(0, 10);  
rectMode(CENTER);  
rect(0, 0, 1000, 1000);  
rect(0, 0, 780, 780, 50);  
rect(0, 0, 790, 790, 50);  
popMatrix();  
save(“iwatch.png”);  
watch = loadImage(“iwatch.png”);

frameRate(2);//2 pics per second

imageMode(CENTER);  
pointer(width/2, height/2, 0);  
}  
float temp = 1;  
drop[] drops;  
drop d1;

boolean temp2 = false;

//start\_loop\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

void draw() {  
//loading frame  
tint(255, 60);  
if (temp==1) delay(2000);  
//looping rain and cloud  
for (TableRow row : table.rows()) {  
index++;  
float flowr0, angle, x0, y0;

```
image(watch, width/2, height/2);
pushMatrix();
temp = pointer(width/2, height/2, temp);
popMatrix();
delay(40);

p = row.getFloat("P");
w = row.getFloat("W");

if (p>=25) flowr0 = 50;
if (p<25) flowr0 = 35;
if (p<10) flowr0 = 20;

angle = w/360;
x0 = 500*cos(angle);
y0 = 500*sin(angle);

drops = append(drops, new drop(x0, y0, -5, 5, flowr0));

for (drop drop : drops) {
  if (drop.update())
    drop.update();
}

if (mousePressed) {
  d1 = new drop(random(500, 1000), random(0, 500), -5, 5, random(10, 50));
  temp2 = true;
}

while (temp2) {
  temp2 = d1.update();
}

if (keyPressed) exit();

```

}  
}

//define\_function\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

float pointer (float x, float y, float i) {  
translate(x, y);  
rotate((i/300)-PI/2);  
noStroke();  
fill(255);  
circle(0, 0, 10);  
quad(-30, 0, 20, 3, 390, 0, 20, -3);  
return i+1;  
}

//define\_class\_drop\_and\_cloud\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

class drop {  
PVector s, v;  
float flowr;  
drop (float x2, float y2, float vx2, float vy2, float f2) {  
s = new PVector(x2, y2);  
v = new PVector(vx2, vy2);  
flowr = f2;  
}

drop (PVector s1, PVector v1, float f1) {  
s = s1;  
v = v1;  
flowr = f1;  
}  
boolean update() {  
s.add(v);  
flowr = flowr\*0.85;  
tint(200, 60);

```
image(dwr, s.x, s.y, 3*flowr, 3*flowr);

//fill(51,102,153);
//circle(s.x,s.y,flowr);
//println("alive");
if (flowr<5) return false;
return true;

```

}  
}

---

<div class="post-metadata">

**Author:** ![NumericPrime](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/numericprime/32/16318_2.png) [@NumericPrime](https://discourse.processing.org/u/NumericPrime)\
**Post date:** [May 18, 2022, 5:10pm UTC](https://discourse.processing.org/t/how-to-add-a-new-item-in-a-arraylist-when-this-class-is-defined-by-myself/36944/2 "2022-05-18T17:10:38Z")

</div>

I can’t test your code for myself but try

```auto
drops= (drop[]) append(drops, new drop(x0, y0, -5, 5, flowr0));

```

(I’ll explain it in another comment)

---

<div class="post-metadata">

**Author:** ![NumericPrime](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/numericprime/32/16318_2.png) [@NumericPrime](https://discourse.processing.org/u/NumericPrime)\
**Post date:** [May 18, 2022, 5:19pm UTC](https://discourse.processing.org/t/how-to-add-a-new-item-in-a-arraylist-when-this-class-is-defined-by-myself/36944/3 "2022-05-18T17:19:21Z")

</div>

Basicly append returns an Object. Processing however doesn’t know it is an array by casting it to (drop[]) you tell Processing that the object returned is in fact an array.

Another thing you could use are ArrayList. It works simular to an array so you can use.

```auto
ArrayList<drop> list;
void setup(){
list=new ArrayList();
}

```

to create your list. You can simply use

```auto
list.add(new drop(...));

```

to “append” your list. To access an element simular to `array[i]` you can use `list.get(i)`  
to override it you can use `list.set(i,..some object...)`.

I hope I could help you!

(PS: Should you want to stick with append you can add this method to avoid the problem with casting to arrays alltogether

```auto
<T> T[] append(T[] array, T... appended) {
  ArrayList<T> lst=new ArrayList();
  for (int i=0; i<array.length; i++) lst.add(array[i]);
  for (int i=0; i<appended.length; i++) lst.add(appended[i]);
  return (T[]) lst.toArray();
} 

```

It also this also allows appending an array with more than one element so things like

```auto
append(new Integer[]{4,1,2},3,6,1)

```

Make an array with 4,1,2,3,6,1 now.)

---

<div class="post-metadata">

**Author:** ![Lee027](https://avatars.discourse-cdn.com/v4/letter/l/e47774/32.png) [@Lee027](https://discourse.processing.org/u/Lee027)\
**Post date:** [May 18, 2022, 6:44pm UTC](https://discourse.processing.org/t/how-to-add-a-new-item-in-a-arraylist-when-this-class-is-defined-by-myself/36944/4 "2022-05-18T18:44:34Z")

</div>

thanks very much!🫡I use your second method and solve it. Arraylist is a very convenient way for this situation.

---

<div class="post-metadata">

**Author:** ![GoToLoop](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/gotoloop/32/86_2.png) [@GoToLoop](https://discourse.processing.org/u/GoToLoop)\
**Post date:** [May 18, 2022, 6:53pm UTC](https://discourse.processing.org/t/how-to-add-a-new-item-in-a-arraylist-when-this-class-is-defined-by-myself/36944/5 "2022-05-18T18:53:14Z")

</div>

> [@NumericPrime](#):
>
> P.S.: Should you want to stick with **append()** you can add this method to avoid the problem with casting to arrays altogether:

Here’s another alternative **append()** based on Arrays.[**copyOf()**](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Arrays.html#copyOf(T%5B%5D,int)):

```auto
static final <T> T[] append(T[] array, final T value) {
  array = expand(array, array.length + 1);
  array[array.length - 1] = value;
  return array;
}

static final <T> T[] expand(final T[] list) {
  return expand(list, list.length << 1);
}

static final <T> T[] expand(final T[] list, final int newSize) {
  return java.util.Arrays.copyOf(list, newSize);
}

```

Those are from a very old [refused pull request](https://github.com/processing/processing/pull/2903) I’ve done almost a decade ago:

> <https://github.com/GoToLoop/processing/blob/patch-8/core/src/processing/core/PApplet.java#L8464-L8468>

> <https://github.com/GoToLoop/processing/blob/patch-8/core/src/processing/core/PApplet.java#L8360-L8366>

---

<div class="post-metadata">

**Author:** ![NumericPrime](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/numericprime/32/16318_2.png) [@NumericPrime](https://discourse.processing.org/u/NumericPrime)\
**Post date:** [May 19, 2022, 1:45pm UTC](https://discourse.processing.org/t/how-to-add-a-new-item-in-a-arraylist-when-this-class-is-defined-by-myself/36944/6 "2022-05-19T13:45:51Z")

</div>

I combined both versions of the append methods into something one can put into a sketch with the posibility to append the array with multiple elements.

```auto
<T> T[] append(T[] array, T... appended) {
  T[] ret=java.util.Arrays.copyOf(array, array.length+appended.length);
  for(int i=0;i<appended.length;i++) ret[array.length+i]=appended[i];
  return ret;
} 

```

---

<div class="post-metadata">

**Author:** ![GoToLoop](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/gotoloop/32/86_2.png) [@GoToLoop](https://discourse.processing.org/u/GoToLoop)\
**Post date:** [May 19, 2022, 2:06pm UTC](https://discourse.processing.org/t/how-to-add-a-new-item-in-a-arraylist-when-this-class-is-defined-by-myself/36944/7 "2022-05-19T14:06:53Z")

</div>

> [@NumericPrime](#):
>
> … with the possibility to append the array with multiple elements.

That would be **cancat()** instead; which would be faster w/ **arrayCopy()**:

> **[concat() / Reference](https://processing.org/reference/concat_.html)**
>
> Concatenates two arrays. For example, concatenating the array { 1, 2, 3 } and the array { 4, 5, 6 } yields { 1, 2, 3, 4, 5, 6 }. Both parameters must be arrays of the same datatype. When u…

> **[arrayCopy() / Reference](https://processing.org/reference/arrayCopy_.html)**
>
> Copies an array (or part of an array) to another array. The src array is copied to the dst array, beginning at the position specified by srcPosition and into the position specifie…

```auto
static final <T> T[] concat(final T[] a, final T... b) {
  final T[] c = expand(a, a.length + b.length);
  System.arraycopy(b, 0, c, a.length, b.length);
  return c;
}

static final <T> T[] append(T[] array, final T value) {
  array = expand(array, array.length + 1);
  array[array.length - 1] = value;
  return array;
}

static final <T> T[] shorten(final T[] list) {
  return expand(list, list.length - 1);
}

static final <T> T[] expand(final T[] list) {
  return expand(list, list.length << 1);
}

static final <T> T[] expand(final T[] list, final int newSize) {
  return java.util.Arrays.copyOf(list, newSize);
}

```

> <https://github.com/GoToLoop/processing/blob/patch-8/core/src/processing/core/PApplet.java#L8981-L8985>