依赖倒置原则 定义：高层模块不应该依赖低层模块，两者都应该依赖其抽象；抽象不应该依赖细节，细节应该依赖抽象以组装电脑为例：存在的问题：现在的电脑只能使用给定的组件，如果要使用其他的，则违背了开闭原则XiJiepublic class XiJie { public void save(String data) { System.out.println("使用希捷硬盘存储数据：" + data); } public String get() { System.out.println("使用希捷硬盘读取数据"); return "数据"; } }Intelpublic class Intel { public void run() { System.out.println("使用Intel cpu"); } }Kingstonpublic class Kingston { public void save() { System.out.println("使用金士顿内存条"); } }Computerpublic class Computer { private XiJie hardDisk; private Intel cpu; private Kingston memory; public XiJie getHardDisk() { return hardDisk; } public void setHardDisk(XiJie hardDisk) { this.hardDisk = hardDisk; } public Intel getCpu() { return cpu; } public void setCpu(Intel cpu) { this.cpu = cpu; } public Kingston getMemory() { return memory; } public void setMemory(Kingston memory) { this.memory = memory; } public void run() { System.out.println("电脑运行了"); String data = hardDisk.get(); System.out.println("从硬盘上获取的数据是：" + data); cpu.run(); memory.save(); } }ComputerDemopublic class ComputerDemo { public static void main(String[] args) { //创建组件对象 XiJie hardDisk = new XiJie(); Intel cpu = new Intel(); Kingston memory = new Kingston(); Computer computer = new Computer(); //组装计算机 computer.setHardDisk(hardDisk); computer.setCpu(cpu); computer.setMemory(memory); //运行 //存在的问题：现在的电脑只能使用给定的组件，如果要使用其他的，则违背了开闭原则 computer.run(); } }改进：抽象出各个配件的接口，让Computer类依赖抽象，而不是依赖于各组件的具体实现类HardDiskpublic interface HardDisk { /** * 存储数据 * * @param data 数据 */ void save(String data); /** * 读取数据 * * @return */ String get(); }Cpupublic interface Cpu { /** * 运行 */ void run(); }Memorypublic interface Memory { /** * 保存 */ void save(); }XiJiepublic class XiJie implements HardDisk { @Override public void save(String data) { System.out.println("使用希捷硬盘存储数据：" + data); } @Override public String get() { System.out.println("使用希捷硬盘读取数据"); return "数据"; } }Intelpublic class Intel implements Cpu { @Override public void run() { System.out.println("使用Intel cpu"); } }AMDpublic class Amd implements Cpu { @Override public void run() { System.out.println("使用AMD cpu"); } }Kingstonpublic class Kingston implements Memory { @Override public void save() { System.out.println("使用金士顿内存条"); } }Computerpublic class Computer { private HardDisk hardDisk; private Cpu cpu; private Memory memory; public HardDisk getHardDisk() { return hardDisk; } public void setHardDisk(HardDisk hardDisk) { this.hardDisk = hardDisk; } public Cpu getCpu() { return cpu; } public void setCpu(Cpu cpu) { this.cpu = cpu; } public Memory getMemory() { return memory; } public void setMemory(Memory memory) { this.memory = memory; } public void run() { System.out.println("电脑运行了"); String data = hardDisk.get(); System.out.println("从硬盘上获取的数据是：" + data); cpu.run(); memory.save(); } }ComputerDemopublic class ComputerDemo { public static void main(String[] args) { //创建组件对象 HardDisk xiJie = new XiJie(); //Cpu intel = new Intel(); Cpu intel = new Amd(); Memory kingston = new Kingston(); //创建计算机对象 Computer computer = new Computer(); //组装计算机 computer.setHardDisk(xiJie); computer.setCpu(intel); computer.setMemory(kingston); //运行 computer.run(); } }