Rebuild-Java/Wildcards.java at master · TeemoJUN/Rebuild-Java · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
package Test_15;

public class Wildcards {
	static void rawArgs(Holder holder,Object obj){
		holder.set(obj);//Warning

		holder.set(new Wildcards());//Warning

	}

	static void unboundedArg(Holder<?> holder,Object arg){
		//holder.set(val);//Error

		//holder.set(new Wildcards());//Error

		Object obj=holder.get();

	}

	static <T> T exact1(Holder<T> holder){
		T t=holder.get();

		return t;
	}

	static <T> T exact2(Holder<T> holder,T arg){
		holder.set(arg);
		T t=holder.get();
		return t;
	}

	static <T> T wildSubtype(Holder<? extends T> holder,T arg){
		//  holder.set(val);//Error

		T t=holder.get();
		return t;
	}

	static <T> void wildSupertype(Holder<? super T> holder,T arg){
		holder.set(arg);

		//T t=holder.get();//Error

		//OK ,but type information has been lost;
		Object obj=holder.get();

	}

	public static void main(String[] args){
		Holder raw=new Holder<Long>();
		//Or:
		raw=new Holder();

		Holder<Long> qualified=new Holder<Long>();
		Holder<?> unbounded=new Holder<Long>();
		Holder<? extends Long> bounded=new Holder<Long>();

		Long lng=1L;

		rawArgs(raw,lng);
		rawArgs(qualified,lng);
		rawArgs(unbounded,lng);
		rawArgs(bounded,lng);


		unboundedArg(raw,lng);
		unboundedArg(qualified,lng);
		unboundedArg(unbounded,lng);
		unboundedArg(bounded,lng);

		//Object r1=exact1(raw);
		//Unchecked conversion from Holder to Holder<T>
		// Unchecked method invocation:exact1(Holder<T>) id applied to (Holder)
		Long r2=exact1(qualified);
		Object r3=exact1(unbounded);//must return Object
		Long r4=exact1(bounded);

		//Long r5=exact2(raw,lng)//Warning:
		//Unchecked conversion from Holder to Holder<Long>
		//Unchecked method invocation: exact2(Holder<T>,T)
		// is applied to (HOlder,Long)

		Long r6=exact2(qualified,lng);

		//ÀàÐÍ²»Åä
		//Long r7=exact2(unbounded,lng);//Error
		//Long r8=exact2(bounded,lng);//Error


		//Long r9=wildSubtype(raw,lng);//Warning


		Long r10=wildSubtype(raw,lng);
		Object r11=wildSubtype(unbounded,lng);
		Long r12=wildSubtype(bounded,lng);


	}

}