使用场景
当我们构建一个对象的时候，这个对象的字段比较多（比如超过四个以上）
而又存在某些字段是可选的不用额外传入进行构造的场景
这个时候我们有这些方式：
这里还是最推荐使用建造者设计模式
传统的设计方式
假设我们要构造一个电脑对象，其中 CPU 和 RAM 是必选的构造参数（符合实际）
折叠构造器
这种方式写的时候爽，但是维护起来难受，在实例化之前需要明白所有构造器的传参规范，都有哪些，构造器内是做什么，后期维护困难
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| public class ConventionalConstructorComputer {
private final String cpu;
private final String ram;
private String display;
private String keyboard;
private String usbCount;
public ConventionalConstructorComputer(String cpu, String ram) {
this.cpu = cpu;
this.ram = ram;
}
public ConventionalConstructorComputer(String cpu, String ram, String display) {
this.cpu = cpu;
this.ram = ram;
this.display = display;
}
public ConventionalConstructorComputer(String cpu, String ram, String display, String keyboard) {
this.cpu = cpu;
this.ram = ram;
this.display = display;
this.keyboard = keyboard;
}
public ConventionalConstructorComputer(String cpu, String ram, String display, String keyboard, String usbCount) {
this.cpu = cpu;
this.ram = ram;
this.display = display;
this.keyboard = keyboard;
this.usbCount = usbCount;
}
}
|
Java Bean
这种就是最基础的 get set 方式
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| public class ConventionalBeanComputer {
private String cpu;
private String ram;
private String display;
private String keyboard;
private String usbCount;
public String getCpu() {
return cpu;
}
public void setCpu(String cpu) {
this.cpu = cpu;
}
public String getRam() {
return ram;
}
public void setRam(String ram) {
this.ram = ram;
}
public String getDisplay() {
return display;
}
public void setDisplay(String display) {
this.display = display;
}
public String getKeyboard() {
return keyboard;
}
public void setKeyboard(String keyboard) {
this.keyboard = keyboard;
}
public String getUsbCount() {
return usbCount;
}
public void setUsbCount(String usbCount) {
this.usbCount = usbCount;
}
}
|
虽然比较简洁而且也便于维护
但是可能会导致对象的其他属性在不可见的情况下被修改
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| public class ConventionalPattern {
public static void main(String[] args) {
ConventionalConstructorComputer computer1 = new ConventionalConstructorComputer("Intel", "16g");
ConventionalConstructorComputer computer2 = new ConventionalConstructorComputer("Intel", "16g", "Display");
ConventionalConstructorComputer computer3 = new ConventionalConstructorComputer("Intel", "16g", "Display", "keyboard");
ConventionalConstructorComputer computer4 = new ConventionalConstructorComputer("Intel", "16g", "Display", "keyboard", "usbCount");
ConventionalBeanComputer beanComputer = new ConventionalBeanComputer();
beanComputer.setCpu("Intel");
beanComputer.setRam("16G");
beanComputer.setDisplay("display");
}
}
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建造者模式使用
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| public class Computer {
private final String cpu;
private final String ram;
private final String display;
private final String keyboard;
private final String usbCount;
private Computer(Builder builder) {
this.cpu = builder.cpu;
this.ram = builder.ram;
this.display = builder.display;
this.keyboard = builder.keyboard;
this.usbCount = builder.usbCount;
}
public static class Builder {
private final String cpu;
private final String ram;
private String display;
private String keyboard;
private String usbCount;
public Builder(String cpu, String ram) {
this.cpu = cpu;
this.ram = ram;
}
public Builder buildDisplay(String display) {
this.display = display;
return this;
}
public Builder buildKeyboard(String keyboard) {
this.keyboard = keyboard;
return this;
}
public Builder buildUsbCount(String usbCount) {
this.usbCount = usbCount;
return this;
}
public Computer build(){
return new Computer(this);
}
}
}
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程序可以调用 builder 的任何一个方法来组装拼接对象的部分可选属性
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| public class BuilderPattern {
public static void main(String[] args) {
Computer intelComputer = new Computer.Builder("INTEL", "16G")
.buildDisplay("DISPLAY")
.build();
Computer amdComputer = new Computer.Builder("AMD", "32G")
.buildKeyboard("Cherry")
.buildDisplay("DISPLAY")
.buildUsbCount("4")
.build();
}
}
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