When it comes to platform strategies in the computer software industry, a unique mechanism to decide the issue has been carved in relief. It can be said as a reason that the uniqueness may be derived from the nature of layered structure consisting of OS, middleware, application and network layers. As for preceding studies, there have been many papers regarding the industry ecosystems' formation, e.g. the theory of indirect network externalities between platform and complementary product and two-sided platform theory as platform-mediated networks. However, a few frameworks providing strategic insights between layers could be recognized plainly. This paper addresses two effective measures as platform strategies in the computer software with layered structure. One is "foreclosure attack" by Eisenmann, Parker & Alstyne (2007) and the other one is "layered intervention" which is newly argued in this paper. They both have something in common with the way of attack leveraging the adjacent layer as a footing. According to Eisenmann, Parker & Alstyne (2007), by leveraging common components and shared user relationships, one platform provider can move into another's market, combining its own functionality with the target's in a multi-platform bundle. In the meanwhile, a layered intervention demonstrates the potentiality getting an advantage over the dominant fight on a same level by interfering in the adjacent position to the competitive layer as a cross-platform functional layer. The paper examines the strategic impact for platform providers though the case of Java and analyses four market aspects i.e. context on attack, targeting, measure executed and result. Consequently, the study about Java's case sheds light on the significance of strategies acting upon between layers and indicates three interesting findings below. Firstly, the dominant layer position has been shifted to the cross-platform layer. Secondly, the existing dominant platform monopolization has been hindered. Lastly, a new ecosystem based on the cross-platform layer has emerged. These points may prove that a layered intervention performs an effective role as a strategic measure. To sum up, the measure of layered intervention may deserve to be propounded as a platform strategy for platform providers aiming at the dominant position in the software industry and introducing complimentary software, such as a sort of middleware with cross-platform functionality.