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Two methods in java.util.Collection create an array from a collection: Object[] toArray() <T> T[] toArray(T[] a) Object[] toArray() can be used as follows: Java SE 5 Set<String> set = new HashSet<String>(); set.add("red"); set.add("blue"); ...

Methods can also have generic type parameters. public class Example { // The type parameter T is scoped to the method // and is independent of type parameters of other methods. public <T> List<T> makeList(T t1, T t2) { List<T> result = new ArrayList<T&...

When we create a button in layout, we can use the android:onClick attribute to reference a method in code to handle clicks. Button <Button android:width="120dp" android:height="wrap_content" android:text="Click me" android:onClick="handleCl...

Java SE 5 Since Java 1.5 you can get a String representation of the contents of the specified array without iterating over its every element. Just use Arrays.toString(Object[]) or Arrays.deepToString(Object[]) for multidimentional arrays: int[] arr = {1, 2, 3, 4, 5}; System.out.println(Arrays.toS...

Java 7 introduced the very useful Files class Java SE 7 import java.nio.file.Files; import java.nio.file.Paths; import java.nio.file.Path; Path path = Paths.get("path/to/file"); try { byte[] data = Files.readAllBytes(path); } catch(IOException e) { e.printStackTrace();...

When we create any View in layout, we can use the android:onClick attribute to reference a method in the associated activity or fragment to handle the click events. XML Layout <Button android:id="@+id/button" ... // onClick should reference the method in your activity or fra...

Dimensions are typically stored in a resource file names dimens.xml. They are defined using a <dimen> element. res/values/dimens.xml <?xml version="1.0" encoding="utf-8"?> <resources> <dimen name="small_padding">5dp</dimen> &l...

If your model has private methods, the databinding library still allows you to access them in your view without using the full name of the method. Data model public class Item { private String name; public String getName() { return name; } } Layout XML <?xml versi...

From the documentation: The exception that is thrown when an application attempts to perform a networking operation on its main thread. This is only thrown for applications targeting the Honeycomb SDK or higher. Applications targeting earlier SDK versions are allowed to do networking on their ma...

In order to compare Strings for equality, you should use the String object's equals or equalsIgnoreCase methods. For example, the following snippet will determine if the two instances of String are equal on all characters: String firstString = "Test123"; String secondString = "Test...

/** * Interface with default method */ public interface Printable { default void printString() { System.out.println( "default implementation" ); } } /** * Class which falls back to default implementation of {@link #printString()} */ public class WithDefault...

You can as well access other interface methods from within your default method. public interface Summable { int getA(); int getB(); default int calculateSum() { return getA() + getB(); } } public class Sum implements Summable { @Override public int get...

Java SE 7 Java 7 introduced the Diamond1 to remove some boiler-plate around generic class instantiation. With Java 7+ you can write: List<String> list = new LinkedList<>(); Where you had to write in previous versions, this: List<String> list = new LinkedList<String>()...

class TrivialClass {} A class consists at a minimum of the class keyword, a name, and a body, which might be empty. You instantiate a class with the new operator. TrivialClass tc = new TrivialClass();

package com.example; import android.os.Bundle; import android.support.annotation.Nullable; import android.util.Log; import android.view.View; import android.view.ViewTreeObserver; public class ExampleActivity extends Activity { @Override protected void onCreate(@Nullable final ...

If you need to produce a JSON string with a value of null like this: { "name":null } Then you have to use the special constant JSONObject.NULL. Functioning example: jsonObject.put("name", JSONObject.NULL);

if (i < 2) { System.out.println("i is less than 2"); } else if (i > 2) { System.out.println("i is more than 2"); } else { System.out.println("i is not less than 2, and not more than 2"); } The if block will only run when i is 1 or less. The else if...

for (int i = 0; i < 100; i++) { System.out.println(i); } The three components of the for loop (separated by ;) are variable declaration/initialization (here int i = 0), the condition (here i < 100), and the increment statement (here i++). The variable declaration is done once as if pl...

int i = 0; while (i < 100) { // condition gets checked BEFORE the loop body executes System.out.println(i); i++; } A while loop runs as long as the condition inside the parentheses is true. This is also called the "pre-test loop" structure because the conditional stateme...

The do...while loop differs from other loops in that it is guaranteed to execute at least once. It is also called the "post-test loop" structure because the conditional statement is performed after the main loop body. int i = 0; do { i++; System.out.println(i); } while (i &l...