2020-01-16 04:07:02 +00:00
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2022-02-15 06:14:58 +00:00
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2020-01-16 04:07:02 +00:00
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< h1 > Lecture for January 25< / h1 >
< h2 > Strings< / h2 >
< p > These are concatenated chars< / p >
< pre > < code class = "language-java" > 'd' + 'o' + 'g' // equivalent to "dog"< / code > < / pre >
< pre > < code class = "language-java" > "straw" + "berry" // strawberry< / code > < / pre >
< p > Strings are denoted by double quotes < code > ""< / code > rather than a string which is denoted by single quotes < code > ''< / code > < / p >
< p > String is not a primitive type, it is a class. Hence, why it is capitalized in Java.< / p >
< p > The < code > java.lang.String< / code > is automatically imported in Java.< / p >
< p > To declare and initialize a String< / p >
< pre > < code class = "language-java" > String name = "Henry";< / code > < / pre >
< p > In memory it appears as< / p >
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< th > H< / th >
< th > 'e'< / th >
< th > 'n'< / th >
< th > 'r'< / th >
< th > 'y'< / th >
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< h3 > String Methods< / h3 >
< pre > < code class = "language-java" > int length()< / code > < / pre >
< pre > < code class = "language-java" > boolean equals(String another)< / code > < / pre >
< pre > < code class = "language-java" > boolean startsWith(String prefix)< / code > < / pre >
< pre > < code class = "language-java" > boolean endsWith(String suffix)< / code > < / pre >
< pre > < code class = "language-java" > String substring(int start, int end)< / code > < / pre >
< pre > < code class = "language-java" > int indexOf(int ch)< / code > < / pre >
< pre > < code class = "language-java" > String toLowerCase()< / code > < / pre >
< h3 > Using String Methods< / h3 >
< pre > < code class = "language-java" > char first = name.charAt(0);< / code > < / pre >
< p > Remember in Java, that it starts counting from zero! If you try to access a letter that doesn't exist, it will produce an < code > IndexOutOfBounds< / code > error.< / p >
< h2 > Errors< / h2 >
< p > 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.< / p >
< h3 > Compile Time Errors< / h3 >
< p > Compile time errors are generated due to syntax errors. Forgot a semicolon? Missing a brace? < / p >
< h3 > Run-time Errors< / h3 >
< p > These are logic errors. Not derived from syntax errors. An example of one that was discussed earlier is the < code > IndexOutOfBounds< / code > error.< / p >
< h2 > Tricky Thing About Input< / h2 >
< p > Let's talk about input right now. Let's say you have the following scenario< / p >
< pre > < code class = "language-java" > 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();< / code > < / pre >
< p > Then when we start to run the program...< / p >
< pre > < code class = "language-reStructuredText" > Enter pet's age:
14
Enter pet's name:
Enter pet's breed:
Labradoodle< / code > < / pre >
< p > Why did it skip pet's name? Let's run through the process again< / p >
< pre > < code class = "language-reStructuredText" > Enter pet's age:
14 [ENTER]
Enter pet's name:
Enter pet's breed:
Labradoodle< / code > < / pre >
< p > Here the [ENTER] key gets saved into name.< / p >
< p > To resolve this, just use an < code > input.nextLine()< / code > to throw away that [ENTER]< / p >
< pre > < code class = "language-java" > 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();< / code > < / pre >
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