How to Resize ImageView by percentage in android - USING JAVA CODE

With every view, android provide an override method(onMeasure) in which there are 2 parameters(int widthMeasureSpec, int heightMeasureSpec), You can return height width according to your requirement. 

Example: If you want height = width means a square size view you can return height and width like this: 

@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
{
    super.onMeasure(heightMeasureSpec, heightMeasureSpec);
}

You can create your custom view for this :

Example: 

Make a class names CustomImageView extends with ImageView

public class CustomImageView extends ImageView
{
    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
    {
        super.onMeasure(heightMeasureSpec, heightMeasureSpec);

        // you can set this as per percentage also. For example: "heightMeasureSpec * 50 /100"  ---- the height will be 50% of the view's width. 
    }
}

Use this in your layout like this :
<CustomImageView    
    android:id="@+id/imageView"    
    android:layout_width="match_parent"    
    android:layout_height="wrap_content"
    android:src="@drawable/ic_launcher"    />