A display device, comprising: a display; a memory; and a processor configured to: run at least one application (410, 420, 440) on the memory, allocate a front window buffer (411, 421, 441) and a back window buffer (413, 423, 443) to each of the at least one application (410, 420, 440) on the memory, wherein the front window buffer (411, 421, 441) is used for storing a first image currently displayed on the display and wherein the back window buffer (413, 423, 443) is used for storing a second image to be displayed on the display after the first image; in a state where the at least one application (410, 420, 440) is running is maintained: collect the back window buffer allocated to an application based on a state where at least a portion of the first image by the application is not displayed on the display, and collect the front window buffer and the back window buffer which are allocated to an application based on a state where all of the first image by the application is not displayed on the display. a display; a memory; and a processor configured to: run at least one application (410, 420, 440) on the memory, allocate a front window buffer (411, 421, 441) and a back window buffer (413, 423, 443) to each of the at least one application (410, 420, 440) on the memory, wherein the front window buffer (411, 421, 441) is used for storing a first image currently displayed on the display and wherein the back window buffer (413, 423, 443) is used for storing a second image to be displayed on the display after the first image; in a state where the at least one application (410, 420, 440) is running is maintained: collect the back window buffer allocated to an application based on a state where at least a portion of the first image by the application is not displayed on the display, and collect the front window buffer and the back window buffer which are allocated to an application based on a state where all of the first image by the application is not displayed on the display. run at least one application (410, 420, 440) on the memory, allocate a front window buffer (411, 421, 441) and a back window buffer (413, 423, 443) to each of the at least one application (410, 420, 440) on the memory, wherein the front window buffer (411, 421, 441) is used for storing a first image currently displayed on the display and wherein the back window buffer (413, 423, 443) is used for storing a second image to be displayed on the display after the first image; in a state where the at least one application (410, 420, 440) is running is maintained: collect the back window buffer allocated to an application based on a state where at least a portion of the first image by the application is not displayed on the display, and collect the front window buffer and the back window buffer which are allocated to an application based on a state where all of the first image by the application is not displayed on the display. collect the back window buffer allocated to an application based on a state where at least a portion of the first image by the application is not displayed on the display, and collect the front window buffer and the back window buffer which are allocated to an application based on a state where all of the first image by the application is not displayed on the display.