Definations And Use :- Annotations

Annotation is Metadata. Metadata is data about data

public class AnnotationsSample {

    protected void execute() {
        Car car = new Car("Ford", "F150", "2018");
        JsonSerializer serializer = new JsonSerializer();
        try {
            serializer.serialize(car);
        } catch (JsonSerializeException e) {
            e.printStackTrace();
        }
    }
}

public class AnnotationsSample {

protected void execute() {

Car car = new Car("Ford", "F150", "2018");

JsonSerializer serializer = new JsonSerializer();

try {

serializer.serialize(car);

} catch (JsonSerializeException e) {

e.printStackTrace();

}

public class Car {
    @JsonField("manufacturer")
    private final String make;
    @JsonField
    private final String model;
    @IgnoreMe
    private final String year;
    public Car(String make, String model, String year) {
        this.make = make;
        this.model = model;
        this.year = year;
    }
    public String getMake() {
        return make;
    }
    public String getModel() {
        return model;
    }
    public String getYear() {
        return year;
    }
    @Override
    public String toString() {
        return year + " " + make + " " + model;
    }
}

public class Car {

@JsonField("manufacturer")

private final String make;

@JsonField

private final String model;

@IgnoreMe

private final String year;

public Car(String make, String model, String year) {

this.make = make;

this.model = model;

this.year = year;

}

public String getMake() {

return make;

}

public String getModel() {

return model;

}

public String getYear() {

return year;

}

@Override

public String toString() {

return year + " " + make + " " + model;

}

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface IgnoreMe {
    String value() default "";
}

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)

@Target(ElementType.FIELD)

public @interface IgnoreMe {

String value() default "";

}

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface JsonField {
    String value() default "";
}

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)

@Target(ElementType.FIELD)

public @interface JsonField {

String value() default "";

}

public class JsonSerializeException extends Exception {
    private static final long serialVersionUID = -8845242379503538623L;

    public JsonSerializeException(String message) {
        super(message);
    }
}

public class JsonSerializeException extends Exception {

private static final long serialVersionUID = -8845242379503538623L;

public JsonSerializeException(String message) {

super(message);

}

import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;



public class JsonSerializer {
    private static String getSerializedKey(Field field) {
        String annotationValue = field.getAnnotation(JsonField.class).value();
        if (annotationValue.isEmpty()) {
            return field.getName();
        } else {
            return annotationValue;
        }
    }

    public String serialize(Object object) throws JsonSerializeException {
        try {
            Class<?> objectClass = requireNonNull(object).getClass();
            Map<String, String> jsonElements = new HashMap<>();
            for (Field field : objectClass.getDeclaredFields()) {

                field.setAccessible(true);
                if (field.isAnnotationPresent(JsonField.class)) {
                    jsonElements.put(getSerializedKey(field), (String) field.get(object));
                } else if (field.isAnnotationPresent(IgnoreMe.class)) {

                } else {
                    jsonElements.put(field.getName(), (String) field.get(object));
                }
            }
            System.out.println(toJsonString(jsonElements));
            return toJsonString(jsonElements);
        } catch (IllegalAccessException e) {
            throw new JsonSerializeException(e.getMessage());
        }
    }

    private Object requireNonNull(Object object) {
        if (object == null) {
            throw new NullPointerException();
        } else {
            return object;
        }

    }

    private String toJsonString(Map<String, String> jsonMap) {


        StringBuilder elementsString = new StringBuilder();
        for (Map.Entry<String, String> entry : jsonMap.entrySet())
            elementsString.append("\"").append(entry.getKey()).append("\":\"").append(entry.getValue()).append("\"");
        return "{" + elementsString + "}";
    }
}

import java.lang.reflect.Field;

import java.util.HashMap;

import java.util.Map;

public class JsonSerializer {

private static String getSerializedKey(Field field) {

String annotationValue = field.getAnnotation(JsonField.class).value();

if (annotationValue.isEmpty()) {

return field.getName();

} else {

return annotationValue;

}

public String serialize(Object object) throws JsonSerializeException {

try {

Class<?> objectClass = requireNonNull(object).getClass();

Map<String, String> jsonElements = new HashMap<>();

for (Field field : objectClass.getDeclaredFields()) {

field.setAccessible(true);

if (field.isAnnotationPresent(JsonField.class)) {

jsonElements.put(getSerializedKey(field), (String) field.get(object));

} else if (field.isAnnotationPresent(IgnoreMe.class)) {

} else {

jsonElements.put(field.getName(), (String) field.get(object));

}

System.out.println(toJsonString(jsonElements));

return toJsonString(jsonElements);

} catch (IllegalAccessException e) {

throw new JsonSerializeException(e.getMessage());

}

private Object requireNonNull(Object object) {

if (object == null) {

throw new NullPointerException();

} else {

return object;

}

private String toJsonString(Map<String, String> jsonMap) {

StringBuilder elementsString = new StringBuilder();

for (Map.Entry<String, String> entry : jsonMap.entrySet())

elementsString.append("\"").append(entry.getKey()).append("\":\"").append(entry.getValue()).append("\"");

return "{" + elementsString + "}";

}

shubham sharma September 11, 2018 Read More

Definations And Use :- Interface

What is Interface An interface in java is a blueprint of a class. Purposes of Interfaces create loosely coupled software support design by contract (an implementor must provide the entire interface) allow for pluggable software allow different objects to interact easily hide implementation details of classes from each other facilitate reuse of software It is used to achieve total […]

shubham sharma September 11, 2018 Read More

Common Issues

ViewPager PagerAdapter not updating the View

public int getItemPosition(Object object) {
    return POSITION_NONE;
}

public int getItemPosition(Object object) {

return POSITION_NONE;

}

shubham sharma September 10, 2018 Read More

ViewPager PagerAdapter not updating the View

There are several ways to achieve this. The first option is easier, but bit more inefficient. Override getItemPosition in your PagerAdapter like this:

public int getItemPosition(Object object) {
    return POSITION_NONE;
}

public int getItemPosition(Object object) {

return POSITION_NONE;

}

This way, when you call notifyDataSetChanged(), the view pager will remove all views and reload them all. As so the reload effect is obtained. The second option, suggested by Alvaro Luis Bustamante (previously alvarolb), is to setTag()method in instantiateItem() when […]

shubham sharma July 20, 2018 Read More

Moving and resizing DrawerLayout’s content on sliding

You can do this by translating and scaling the content View in the onDrawerSlide() method of a DrawerListener on your DrawerLayout. Since the content View itself is resizing, and there’s a separate TextView that appears in the bottom right corner, we’ll stick both of these in another holder ViewGroup. If that label TextView isn’t needed, the holder ViewGroup can be omitted, as well. A basic DrawerLayout setup for the example:

<android.support.v4.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#222222">

    <RelativeLayout android:id="@+id/holder"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <LinearLayout android:id="@+id/content"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">

            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                android:background="#E97411" />

            <ImageView android:id="@+id/main_content"
                android:layout_width="match_parent"
                android:layout_height="0dp"
                android:layout_weight="1"
                android:background="#EEEEEE"
                android:src="@drawable/ic_launcher" />

        </LinearLayout>

        <TextView android:id="@+id/label"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:layout_alignParentRight="true"
            android:visibility="gone"
            android:textSize="26dp"
            android:text="My App" />

    </RelativeLayout>

    <android.support.design.widget.NavigationView
        android:id="@+id/navigation_view"
        android:layout_width="240dp"
        android:layout_height="match_parent"
        android:layout_gravity="left"
        android:background="#555555" />

</android.support.v4.widget.DrawerLayout>

<android.support.v4.widget.DrawerLayout

xmlns:android="http://schemas.android.com/apk/res/android"

android:id="@+id/drawer_layout"