准备工作

有下面这样一个类结构

class R1 {
	
	private String t1;

	public R1(String t1) {
		this.t1 = t1;
	}

	public String getT1() {
		return t1;
	}

	public void setT1(String t1) {
		this.t1 = t1;
	}
	
}

class R2 {
	
	private R1 r1;

	public R2(R1 r1) {
		this.r1 = r1;
	}

	public R1 getR1() {
		return r1;
	}

	public void setR1(R1 r1) {
		this.r1 = r1;
	}
	
}

class R3 {
	
	private R2 r2;

	public R3(R2 r2) {
		this.r2 = r2;
	}

	public R2 getR2() {
		return r2;
	}

	public void setR2(R2 r2) {
		this.r2 = r2;
	}
	
}

class R4 {
	
	private R3 r3;

	public R4(R3 r3) {
		this.r3 = r3;
	}

	public R3 getR3() {
		return r3;
	}

	public void setR3(R3 r3) {
		this.r3 = r3;
	}
	
}

从R4对象中取出R1对象中的t1的值，并打印。其中任意对象可能为null。你会怎么做？

套娃？

private static void nested(R4 r4) {
		String result = null;
		if (r4 != null) {
			R3 r3 = r4.getR3();
			if (r3 != null) {
				R2 r2 = r3.getR2();
				if (r2 != null) {
					R1 r1 = r2.getR1();
					if (r1 != null) {
						result = r1.getT1();
					}
				}
			}
		}
		System.out.println("nested->" + result);
	}

禁止套娃，技术太菜，开除了吧

lambda表达式取值？

private static void lambda(R4 r4) {
		String result = Optional.ofNullable(r4)
				.map(e -> e.getR3())
				.map(e -> e.getR2())
				.map(e -> e.getR1())
				.map(e -> e.getT1())
				.orElse(null);
		System.out.println("lambda->" + result);
	}

技术不错，可是老项目还在用java6或7

封装单独的方法？

private static void methodReturn(R4 r4) {
		class RetClazz {
			public String returnVal (R4 r4) {
				if (r4 == null) {
					return null;
				}
				R3 r3 = r4.getR3();
				if (r3 == null) {
					return null;
				}
				R2 r2 = r3.getR2();
				if (r2 == null) {
					return null;
				}
				R1 r1 = r2.getR1();
				if (r1 == null) {
					return null;
				}
				return r1.getT1();
			}
		}
		String result = new RetClazz().returnVal(r4);
		System.out.println("methodReturn->" + result);
	}

懂得封装，技术不错

do while (false) 是什么鬼？

private static void dowhile(R4 r4) {
		String result = null;
		do {
			if (r4 == null) {
				break;
			}
			R3 r3 = r4.getR3();
			if (r3 == null) {
				break;
			}
			R2 r2 = r3.getR2();
			if (r2 == null) {
				break;
			}
			R1 r1 = r2.getR1();
			if (r1 == null) {
				break;
			}
			result = r1.getT1();
		} while (false);
		System.out.println("dowhile->" + result);
	}

小伙子思路清奇，竟然用循环结构的break关键字，java大神要review你的代码，看你出什么妖蛾子，质量太差就开除你；C大神，嗯，这才是好码农，支持一波

这时需求变了，从R4对象中取出R1对象中的t1的值，并打印，但是当R2为null时，执行printR2null方法且不打印t1的值。其中任意对象可能为null

private static void printR2null (String method) {
		System.out.println(method + ": r2==null");
	}

我还套娃

private static void nested2(R4 r4) {
		String result = null;
		if (r4 != null) {
			R3 r3 = r4.getR3();
			if (r3 != null) {
				R2 r2 = r3.getR2();
				if (r2 != null) {
					R1 r1 = r2.getR1();
					if (r1 != null) {
						result = r1.getT1();
					}
				} else {
					printR2null("nested");
					return;
				}
			}
		}
		System.out.println("nested->" + result);
	}

虽然if嵌套太深，但好歹只加一两行代码就实现了

看我lambda大法

private static void lambda2(R4 r4) {
		boolean[] r2null = {false};
		String result = Optional.ofNullable(r4)
				.map(e -> e.getR3())
				.map(e -> {
					R2 r2 = e.getR2();
					r2null[0] = true;
					return r2;
				})
				.map(e -> e.getR1())
				.map(e -> e.getT1())
				.orElse(null);
		if (r2null[0]) {
			printR2null("lambda");
			return;
		}
		System.out.println("lambda->" + result);
	}

什么鬼东西？还定义一个数组对象？普通对象行吗？行。
定义一个boolean类型的变量不行吗？呃，这个真不行，在lambda方法体内引用外面的变量就相当于在内部类中引用外面的final变量，看IDE报了个语法错误，气得java程序员直抓狂，为什么java不支持地址传递

还是封装单独的方法好用

private static void methodReturn2(R4 r4) {
		class RetClazz {
			public Map<String, Object> returnVal (R4 r4) {
				Map<String, Object> map = new HashMap<>();
				if (r4 == null) {
					map.put("result", null);
					return map;
				}
				R3 r3 = r4.getR3();
				if (r3 == null) {
					map.put("result", null);
					return map;
				}
				R2 r2 = r3.getR2();
				if (r2 == null) {
					map.put("nullObject", R2.class);
					map.put("result", null);
					return map;
				}
				R1 r1 = r2.getR1();
				if (r1 == null) {
					map.put("result", null);
					return map;
				}
				map.put("result", r1.getT1());
				return map;
			}
		}
		Map<String, Object> map = new RetClazz().returnVal(r4);
		Object result = map.get("nullObject");
		if (result instanceof R2) {
			printR2null("methodReturn");
			return;
		}
		System.out.println("methodReturn->" + map.get("result"));
	}

你又搞什么鬼，返回值怎么变成对象了？不过好歹比前面的方法看着舒服点，就这样吧，以后需求变动就让你改。

do while (false) 再次出场

private static void dowhile2(R4 r4) {
		String result = null;
		do {
			if (r4 == null) {
				break;
			}
			R3 r3 = r4.getR3();
			if (r3 == null) {
				break;
			}
			R2 r2 = r3.getR2();
			if (r2 == null) {
				printR2null("dowhile");
				return;
			}
			R1 r1 = r2.getR1();
			if (r1 == null) {
				break;
			}
			result = r1.getT1();
		} while (false);
		System.out.println("dowhile->" + result);
	}