Lecture for January 25

Strings

These are concatenated chars

'd' + 'o' + 'g' // equivalent to "dog"

"straw" + "berry" // strawberry

Strings are denoted by double quotes "" rather than a string which is denoted by single quotes ''

String is not a primitive type, it is a class. Hence, why it is capitalized in Java.

The java.lang.String is automatically imported in Java.

To declare and initialize a String

String name = "Henry";

In memory it appears as

String Methods

int length()

boolean equals(String another)

boolean startsWith(String prefix)

boolean endsWith(String suffix)

String substring(int start, int end)

int indexOf(int ch)

String toLowerCase()

Using String Methods

char first = name.charAt(0);

Remember in Java, that it starts counting from zero! If you try to access a letter that doesn’t exist, it will produce an IndexOutOfBounds error.

Errors

There are two types of errors, compile-type errors and run-time errors. Later we will talk about debugging skills such as making “breakpoints” in your code so you can analyze the different variable values.

Compile Time Errors

Compile time errors are generated due to syntax errors. Forgot a semicolon? Missing a brace?

Run-time Errors

These are logic errors. Not derived from syntax errors. An example of one that was discussed earlier is the IndexOutOfBounds error.

Tricky Thing About Input

Let’s talk about input right now. Let’s say you have the following scenario

Scanner input = new Scanner(System.in);
System.out.println("Enter pet's age: ");
int age = input.nextInt();
System.out.println("Enter pet's name: ");
String name = input.nextLine();
System.out.println("Enter pet's breed: ");
String breed = input.next();

Then when we start to run the program…

Enter pet's age: 
14
Enter pet's name:
Enter pet's breed:
Labradoodle

Why did it skip pet’s name? Let’s run through the process again

Enter pet's age: 
14 [ENTER]
Enter pet's name:
Enter pet's breed:
Labradoodle

Here the [ENTER] key gets saved into name.

To resolve this, just use an input.nextLine() to throw away that [ENTER]

Scanner input = new Scanner(System.in);
System.out.println("Enter pet's age: ");
int age = input.nextInt();
System.out.println("Enter pet's name: ");
input.nextLine();
String name = input.nextLine();
System.out.println("Enter pet's breed: ");
String breed = input.next();