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137 lines
2.7 KiB
Markdown
137 lines
2.7 KiB
Markdown
# Lecture for January 25
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## Strings
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These are concatenated chars
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```java
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'd' + 'o' + 'g' // equivalent to "dog"
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```
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```java
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"straw" + "berry" // strawberry
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```
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Strings are denoted by double quotes `""` rather than a string which is denoted by single quotes `''`
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String is not a primitive type, it is a class. Hence, why it is capitalized in Java.
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The `java.lang.String` is automatically imported in Java.
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To declare and initialize a String
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```java
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String name = "Henry";
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```
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In memory it appears as
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| H | 'e' | 'n' | 'r' | 'y' |
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| ---- | ---- | ---- | ---- | ---- |
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| | | | | |
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### String Methods
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```java
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int length()
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```
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```java
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boolean equals(String another)
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```
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```java
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boolean startsWith(String prefix)
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```
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```java
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boolean endsWith(String suffix)
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```
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```java
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String substring(int start, int end)
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```
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```java
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int indexOf(int ch)
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```
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```java
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String toLowerCase()
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```
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### Using String Methods
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```java
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char first = name.charAt(0);
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```
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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.
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## Errors
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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.
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### Compile Time Errors
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Compile time errors are generated due to syntax errors. Forgot a semicolon? Missing a brace?
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### Run-time Errors
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These are logic errors. Not derived from syntax errors. An example of one that was discussed earlier is the `IndexOutOfBounds` error.
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## Tricky Thing About Input
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Let's talk about input right now. Let's say you have the following scenario
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```java
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Scanner input = new Scanner(System.in);
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System.out.println("Enter pet's age: ");
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int age = input.nextInt();
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System.out.println("Enter pet's name: ");
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String name = input.nextLine();
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System.out.println("Enter pet's breed: ");
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String breed = input.next();
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```
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Then when we start to run the program...
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```reStructuredText
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Enter pet's age:
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14
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Enter pet's name:
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Enter pet's breed:
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Labradoodle
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```
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Why did it skip pet's name? Let's run through the process again
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```reStructuredText
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Enter pet's age:
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14 [ENTER]
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Enter pet's name:
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Enter pet's breed:
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Labradoodle
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```
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Here the [ENTER] key gets saved into name.
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To resolve this, just use an `input.nextLine()` to throw away that [ENTER]
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```java
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Scanner input = new Scanner(System.in);
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System.out.println("Enter pet's age: ");
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int age = input.nextInt();
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System.out.println("Enter pet's name: ");
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input.nextLine();
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String name = input.nextLine();
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System.out.println("Enter pet's breed: ");
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String breed = input.next();
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```
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