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Arrays are Java's version of lists, and unfortunately they are a bit more difficult to deal with. First, the Java compiler likes to do a bunch of space optimization, so it needs to know how big the value in each variable is going to be during its lifetime. Thus, when you create an array, you have to specify both the type elements are going have as well as the number of cells. The most common way to do this is without specifying the values of the elements:
public static void main(String[] args) {
System.out.println("Hello, World!");
int[] odds = new int[5];
}
odds now has type int[], meaning it will be an array of int values. The array has five cells, so it will be able to hold five values. We can initialize those values by adding some assignment statements. These look almost exactly the same as in Python:
public static void main(String[] args) {
System.out.println("Hello, World!");
int[] odds = new int[5];
odds[0] = 1;
odds[1] = 3;
odds[2] = 5;
odds[3] = 7;
odds[4] = 9;
System.out.println("odds: " + odds);
}
Note that just like Python, Java indexes starting from 0. If we wanted to do this all in one line, we can! To do this, we still have to use the keyword new, but drop the size argument and add the elements in squiggly braces:
public static void main(String[] args) {
System.out.println("Hello, World!");
int[] odds = new int[] {1, 3, 5, 7, 9};
System.out.println("odds: " + odds);
}
Let's try running that code:
$ javac *.java
$ java CodeToRun
Hello, World!
odds: [I@7852e922
What? That doesn't look like what we want because there is no toString method for arrays. (Arrays are some sort of not-quite a class in Java. Like Python, they have fields. Unlike Python, there are no array methods!) The weird things printed out correspond to the address the array is stored at. We can access single elements easily, though:
public static void main(String[] args) {
System.out.println("Hello, World!");
int[] odds = new int[] {1, 3, 5, 7, 9};
System.out.println("odds: " + odds);
System.out.println("odds[2] (should be 5): " + odds[2]);
}
In order to nicely print out the entire array, we need to write a loop. Our for loop to traverse the array will look a lot like the one to traverse a string, except that we can't use the length() method because there isn't one for arrays. Instead, we have to use the length field. Additionally, I'm using print instead of println in some lines. It's the same thing, except it doesn't go to a new line at the end.
public static void main(String[] args) {
System.out.println("Hello, World!");
int[] odds = new int[] {1, 3, 5, 7, 9};
System.out.print("[");
for (int i = 0; i < odds.length; i++) {
System.out.print(odds[i] + ", ");
}
System.out.println("]");
}
Running this gives us:
$ javac *.java
$ java CodeToRun
Hello, World!
odds: [1, 3, 5, 7, 9, ]
Removing that extra comma can be attained by adding a conditional inside the loop:
public static void main(String[] args) {
System.out.println("Hello, World!");
int[] odds = new int[] {1, 3, 5, 7, 9};
System.out.print("[");
for (int i = 0; i < odds.length; i++) {
System.out.print(odds[i]);
if (i < odds.length - 1) {
System.out.print(", ");
}
}
System.out.println("]");
}
Unfortunately, there is no way to change the size of an array once it has been created. In order to do something like Python's odds.append(11), you have to create a whole new array:
public static void main(String[] args) {
System.out.println("Hello, World!");
int[] odds = new int[] {1, 3, 5, 7, 9};
//temporary variable for the new array
int[] moreOdds = new int[odds.length + 1];
//copy the old elements over to moreOdds
for (int i = 0; i < odds.length; i ++) {
moreOdds[i] = odds[i];
}
//add the new element to the end of moreOdds
moreOdds[moreOdds.length - 1] = 11;
//reassign the odds variable to the new array
odds = moreOdds;
}
In your Monkey class, add another parameter to your printMonkey method, an array of strings, bananas, where each string describes another banana that the monkey has. Your method should print out the bananas using a for loop. Create string arrays in your main method and pass one to each of the printMonkey calls. My code's output looks like this: (notice that it specifies the number of bananas)
$ javac *.java $ java Monkey Pongiona is a funny monkey with 4 teeth and a 26.34-inch long tail. Pongiona has a bunch of 4 bananas: * green * yellow * green * brown Jasmine Boreal is not a funny monkey with 32 teeth and a 2.0-inch long tail. Jasmine Boreal has a bunch of 3 bananas: * yellow * green * bananaphone