这是递归吗？
public class Test {
Test test = new Test();
public static void main(String[] args) {
new Test();
}
}
instance initalizer的版本怎么样？
public class Test {
{ Test test = new Test(); }
public static void main(String[] args) {
new Test();
}
}
我问，因为我更新了my old answer，其中显示了如何在没有递归的情况下制作StackOverflowError，但现在我不能100％确定上面的代码是递归还是不递归。
答案 0 :(得分：3)
我的观点是它是递归。尽管如此，我无法找到好的消息来源。所以我试图将已知递归函数的汇编代码与OP中生成的java代码汇编代码进行比较。两个汇编代码非常相似，在调用自身的方法（构造函数）时会出现这个问题。
我的测试代码：
public class Test3 {
void printMe() {
printMe();
}
public static void main(String[] args) {
Test3 test = new Test3();
test.printMe();
}
}
打印组件：
java -XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly -server -cp . Test3
相关汇编代码序列，显示函数调用自身：
Decoding compiled method 0x00007f2e2910ac90:
Code:
[Entry Point]
[Constants]
# {method} {0x00007f2e27121230} 'printMe' '()V' in 'com/vs/soutils/Test3'
# [sp+0x40] (sp of caller)
0x00007f2e2910ae00: mov 0x8(%rsi),%r10d
0x00007f2e2910ae04: shl $0x3,%r10
0x00007f2e2910ae08: cmp %rax,%r10
0x00007f2e2910ae0b: jne 0x00007f2e29045b60 ; {runtime_call}
0x00007f2e2910ae11: nopw 0x0(%rax,%rax,1)
0x00007f2e2910ae1c: xchg %ax,%ax
[Verified Entry Point]
0x00007f2e2910ae20: mov %eax,-0x14000(%rsp)
0x00007f2e2910ae27: push %rbp
0x00007f2e2910ae28: sub $0x30,%rsp
0x00007f2e2910ae2c: mov $0x7f2e271213f8,%rdi ; {metadata(method data for {method} {0x00007f2e27121230} 'printMe' '()V' in 'com/vs/soutils/Test3')}
0x00007f2e2910ae36: mov 0x64(%rdi),%ebx
0x00007f2e2910ae39: add $0x8,%ebx
0x00007f2e2910ae3c: mov %ebx,0x64(%rdi)
0x00007f2e2910ae3f: mov $0x7f2e27121230,%rdi ; {metadata({method} {0x00007f2e27121230} 'printMe' '()V' in 'com/vs/soutils/Test3')}
0x00007f2e2910ae49: and $0x1ff8,%ebx
0x00007f2e2910ae4f: cmp $0x0,%ebx
0x00007f2e2910ae52: je 0x00007f2e2910aec0 ;*aload_0
; - com.vs.soutils.Test3::printMe@0 (line 6)
0x00007f2e2910ae58: mov %rsi,%rdi
0x00007f2e2910ae5b: mov $0x7f2e271213f8,%rbx ; {metadata(method data for {method} {0x00007f2e27121230} 'printMe' '()V' in 'com/vs/soutils/Test3')}
0x00007f2e2910ae65: addq $0x1,0xa0(%rbx)
0x00007f2e2910ae6d: mov $0x7f2e271213f8,%rdi ; {metadata(method data for {method} {0x00007f2e27121230} 'printMe' '()V' in 'com/vs/soutils/Test3')}
0x00007f2e2910ae77: mov 0x64(%rdi),%ebx
0x00007f2e2910ae7a: add $0x8,%ebx
0x00007f2e2910ae7d: mov %ebx,0x64(%rdi)
0x00007f2e2910ae80: mov $0x7f2e27121230,%rdi ; {metadata({method} {0x00007f2e27121230} 'printMe' '()V' in 'com/vs/soutils/Test3')}
0x00007f2e2910ae8a: and $0x7ffff8,%ebx
0x00007f2e2910ae90: cmp $0x0,%ebx
0x00007f2e2910ae93: je 0x00007f2e2910aed4
0x00007f2e2910ae99: mov %rsi,%rdi
0x00007f2e2910ae9c: mov $0x7f2e271213f8,%rbx ; {metadata(method data for {method} {0x00007f2e27121230} 'printMe' '()V' in 'com/vs/soutils/Test3')}
0x00007f2e2910aea6: addq $0x1,0xa0(%rbx)
0x00007f2e2910aeae: nop
0x00007f2e2910aeaf: callq 0x00007f2e29045d60 ; OopMap{off=180}
;*invokevirtual printMe
; - com.vs.soutils.Test3::printMe@1 (line 6)
; - com.vs.soutils.Test3::printMe@1 (line 6)
; {optimized virtual_call}
0x00007f2e2910aeb4: add $0x30,%rsp
0x00007f2e2910aeb8: pop %rbp
0x00007f2e2910aeb9: test %eax,0x16461241(%rip) # 0x00007f2e3f56c100
; {poll_return}
0x00007f2e2910aebf: retq
0x00007f2e2910aec0: mov %rdi,0x8(%rsp)
0x00007f2e2910aec5: movq $0xffffffffffffffff,(%rsp)
0x00007f2e2910aecd: callq 0x00007f2e290fdde0 ; OopMap{rsi=Oop off=210}
;*synchronization entry
; - com.vs.soutils.Test3::printMe@-1 (line 6)
; {runtime_call}
0x00007f2e2910aed2: jmp 0x00007f2e2910ae58
0x00007f2e2910aed4: mov %rdi,0x8(%rsp)
0x00007f2e2910aed9: movq $0xffffffffffffffff,(%rsp)
0x00007f2e2910aee1: callq 0x00007f2e290fdde0 ; OopMap{rsi=Oop off=230}
;*synchronization entry
; - com.vs.soutils.Test3::printMe@-1 (line 6)
; - com.vs.soutils.Test3::printMe@1 (line 6)
; {runtime_call}
0x00007f2e2910aee6: jmp 0x00007f2e2910ae99
0x00007f2e2910aee8: nop
0x00007f2e2910aee9: nop
0x00007f2e2910aeea: mov 0x288(%r15),%rax
0x00007f2e2910aef1: mov $0x0,%r10
0x00007f2e2910aefb: mov %r10,0x288(%r15)
0x00007f2e2910af02: mov $0x0,%r10
0x00007f2e2910af0c: mov %r10,0x290(%r15)
0x00007f2e2910af13: add $0x30,%rsp
0x00007f2e2910af17: pop %rbp
0x00007f2e2910af18: jmpq 0x00007f2e2906be20 ; {runtime_call}
现在将它与原始代码的汇编代码进行比较：
Decoding compiled method 0x00007fea24ef0dd0:
Code:
[Entry Point]
[Constants]
# {method} {0x00007fea229431b0} '<init>' '()V' in 'com/vs/soutils/Test'
# [sp+0x80] (sp of caller)
0x00007fea24ef0f60: mov 0x8(%rsi),%r10d
0x00007fea24ef0f64: shl $0x3,%r10
0x00007fea24ef0f68: cmp %rax,%r10
0x00007fea24ef0f6b: jne 0x00007fea24e29b60 ; {runtime_call}
0x00007fea24ef0f71: nopw 0x0(%rax,%rax,1)
0x00007fea24ef0f7c: xchg %ax,%ax
[Verified Entry Point]
0x00007fea24ef0f80: mov %eax,-0x14000(%rsp)
0x00007fea24ef0f87: push %rbp
0x00007fea24ef0f88: sub $0x70,%rsp
0x00007fea24ef0f8c: mov $0x7fea22943350,%rdx ; {metadata(method data for {method} {0x00007fea229431b0} '<init>' '()V' in 'com/vs/soutils/Test')}
0x00007fea24ef0f96: mov 0x64(%rdx),%edi
0x00007fea24ef0f99: add $0x8,%edi
0x00007fea24ef0f9c: mov %edi,0x64(%rdx)
0x00007fea24ef0f9f: mov $0x7fea229431b0,%rdx ; {metadata({method} {0x00007fea229431b0} '<init>' '()V' in 'com/vs/soutils/Test')}
0x00007fea24ef0fa9: and $0x1ff8,%edi
0x00007fea24ef0faf: cmp $0x0,%edi
0x00007fea24ef0fb2: je 0x00007fea24ef1172 ;*aload_0
; - com.vs.soutils.Test::<init>@0 (line 3)
0x00007fea24ef0fb8: mov %rsi,%rdx
0x00007fea24ef0fbb: mov $0x7fea22943350,%rdi ; {metadata(method data for {method} {0x00007fea229431b0} '<init>' '()V' in 'com/vs/soutils/Test')}
0x00007fea24ef0fc5: addq $0x1,0x90(%rdi)
0x00007fea24ef0fcd: mov $0x7fea226a1f10,%rdx ; {metadata(method data for {method} {0x00007fea22543488} '<init>' '()V' in 'java/lang/Object')}
0x00007fea24ef0fd7: mov 0x64(%rdx),%edi
0x00007fea24ef0fda: add $0x8,%edi
0x00007fea24ef0fdd: mov %edi,0x64(%rdx)
0x00007fea24ef0fe0: mov $0x7fea22543488,%rdx ; {metadata({method} {0x00007fea22543488} '<init>' '()V' in 'java/lang/Object')}
0x00007fea24ef0fea: and $0x7ffff8,%edi
0x00007fea24ef0ff0: cmp $0x0,%edi
0x00007fea24ef0ff3: je 0x00007fea24ef1189
0x00007fea24ef0ff9: mov $0x7c0060028,%rdx ; {metadata('com/vs/soutils/Test')}
0x00007fea24ef1003: mov %rsi,0x58(%rsp)
0x00007fea24ef1008: mov 0x60(%r15),%rax
0x00007fea24ef100c: lea 0x10(%rax),%rdi
0x00007fea24ef1010: cmp 0x70(%r15),%rdi
0x00007fea24ef1014: ja 0x00007fea24ef11a0
0x00007fea24ef101a: mov %rdi,0x60(%r15)
0x00007fea24ef101e: mov 0xa8(%rdx),%rcx
0x00007fea24ef1025: mov %rcx,(%rax)
0x00007fea24ef1028: mov %rdx,%rcx
0x00007fea24ef102b: shr $0x3,%rcx
0x00007fea24ef102f: mov %ecx,0x8(%rax)
0x00007fea24ef1032: xor %rcx,%rcx
0x00007fea24ef1035: mov %ecx,0xc(%rax)
0x00007fea24ef1038: xor %rcx,%rcx ;*new ; - com.vs.soutils.Test::<init>@5 (line 5)
0x00007fea24ef103b: mov %rax,%rdx
0x00007fea24ef103e: mov $0x7fea22943350,%rsi ; {metadata(method data for {method} {0x00007fea229431b0} '<init>' '()V' in 'com/vs/soutils/Test')}
0x00007fea24ef1048: addq $0x1,0xa0(%rsi)
0x00007fea24ef1050: mov $0x7fea22943350,%rdx ; {metadata(method data for {method} {0x00007fea229431b0} '<init>' '()V' in 'com/vs/soutils/Test')}
0x00007fea24ef105a: mov 0x64(%rdx),%esi
0x00007fea24ef105d: add $0x8,%esi
0x00007fea24ef1060: mov %esi,0x64(%rdx)
0x00007fea24ef1063: mov $0x7fea229431b0,%rdx ; {metadata({method} {0x00007fea229431b0} '<init>' '()V' in 'com/vs/soutils/Test')}
0x00007fea24ef106d: and $0x7ffff8,%esi
0x00007fea24ef1073: cmp $0x0,%esi
0x00007fea24ef1076: je 0x00007fea24ef11ad
0x00007fea24ef107c: mov %rax,%rdx
0x00007fea24ef107f: mov $0x7fea22943350,%rsi ; {metadata(method data for {method} {0x00007fea229431b0} '<init>' '()V' in 'com/vs/soutils/Test')}
0x00007fea24ef1089: addq $0x1,0x90(%rsi)
0x00007fea24ef1091: mov $0x7fea226a1f10,%rdx ; {metadata(method data for {method} {0x00007fea22543488} '<init>' '()V' in 'java/lang/Object')}
0x00007fea24ef109b: mov 0x64(%rdx),%esi
0x00007fea24ef109e: add $0x8,%esi
0x00007fea24ef10a1: mov %esi,0x64(%rdx)
0x00007fea24ef10a4: mov $0x7fea22543488,%rdx ; {metadata({method} {0x00007fea22543488} '<init>' '()V' in 'java/lang/Object')}
0x00007fea24ef10ae: and $0x7ffff8,%esi
0x00007fea24ef10b4: cmp $0x0,%esi
0x00007fea24ef10b7: je 0x00007fea24ef11c4
0x00007fea24ef10bd: mov $0x7c0060028,%rdx ; {metadata('com/vs/soutils/Test')}
0x00007fea24ef10c7: mov %rax,0x50(%rsp)
0x00007fea24ef10cc: mov 0x60(%r15),%rax
0x00007fea24ef10d0: lea 0x10(%rax),%rdi
0x00007fea24ef10d4: cmp 0x70(%r15),%rdi
0x00007fea24ef10d8: ja 0x00007fea24ef11db
0x00007fea24ef10de: mov %rdi,0x60(%r15)
0x00007fea24ef10e2: mov 0xa8(%rdx),%rcx
0x00007fea24ef10e9: mov %rcx,(%rax)
0x00007fea24ef10ec: mov %rdx,%rcx
0x00007fea24ef10ef: shr $0x3,%rcx
0x00007fea24ef10f3: mov %ecx,0x8(%rax)
0x00007fea24ef10f6: xor %rcx,%rcx
0x00007fea24ef10f9: mov %ecx,0xc(%rax)
0x00007fea24ef10fc: xor %rcx,%rcx ;*new ; - com.vs.soutils.Test::<init>@5 (line 5)
; - com.vs.soutils.Test::<init>@9 (line 5)
0x00007fea24ef10ff: mov %rax,%rsi
0x00007fea24ef1102: mov $0x7fea22943350,%rdi ; {metadata(method data for {method} {0x00007fea229431b0} '<init>' '()V' in 'com/vs/soutils/Test')}
0x00007fea24ef110c: addq $0x1,0xa0(%rdi)
0x00007fea24ef1114: mov %rax,%rsi ;*invokespecial <init>
; - com.vs.soutils.Test::<init>@9 (line 5)
; - com.vs.soutils.Test::<init>@9 (line 5)
0x00007fea24ef1117: mov %rax,0x48(%rsp)
0x00007fea24ef111c: nop
0x00007fea24ef111d: nop
0x00007fea24ef111e: nop
0x00007fea24ef111f: callq 0x00007fea24e29d60 ; OopMap{[72]=Oop [80]=Oop [88]=Oop off=452}
;*invokespecial <init>
; - com.vs.soutils.Test::<init>@9 (line 5)
; - com.vs.soutils.Test::<init>@9 (line 5)
; {optimized virtual_call}
0x00007fea24ef1124: mov 0x48(%rsp),%rsi
0x00007fea24ef1129: mov 0x50(%rsp),%rax
0x00007fea24ef112e: mov %rsi,%r10
0x00007fea24ef1131: shr $0x3,%r10
0x00007fea24ef1135: mov %r10d,0xc(%rax)
0x00007fea24ef1139: mov %rax,%rsi
0x00007fea24ef113c: shr $0x9,%rsi
0x00007fea24ef1140: mov $0x7fea20c23000,%rdi
0x00007fea24ef114a: movb $0x0,(%rsi,%rdi,1) ;*putfield test
; - com.vs.soutils.Test::<init>@12 (line 5)
; - com.vs.soutils.Test::<init>@9 (line 5)
0x00007fea24ef114e: mov 0x58(%rsp),%rsi
0x00007fea24ef1153: mov %rax,%r10
0x00007fea24ef1156: shr $0x3,%r10
0x00007fea24ef115a: mov %r10d,0xc(%rsi)
0x00007fea24ef115e: shr $0x9,%rsi
0x00007fea24ef1162: movb $0x0,(%rsi,%rdi,1) ;*putfield test
; - com.vs.soutils.Test::<init>@12 (line 5)
0x00007fea24ef1166: add $0x70,%rsp
0x00007fea24ef116a: pop %rbp
0x00007fea24ef116b: test %eax,0x15e21f8f(%rip) # 0x00007fea3ad13100
; {poll_return}
0x00007fea24ef1171: retq
0x00007fea24ef1172: mov %rdx,0x8(%rsp)
0x00007fea24ef1177: movq $0xffffffffffffffff,(%rsp)
0x00007fea24ef117f: callq 0x00007fea24ee1d20 ; OopMap{rsi=Oop off=548}
;*synchronization entry
; - com.vs.soutils.Test::<init>@-1 (line 3)
; {runtime_call}
0x00007fea24ef1184: jmpq 0x00007fea24ef0fb8
0x00007fea24ef1189: mov %rdx,0x8(%rsp)
0x00007fea24ef118e: movq $0xffffffffffffffff,(%rsp)
0x00007fea24ef1196: callq 0x00007fea24ee1d20 ; OopMap{rsi=Oop off=571}
;*synchronization entry
; - java.lang.Object::<init>@-1 (line 37)
; - com.vs.soutils.Test::<init>@1 (line 3)
; {runtime_call}
0x00007fea24ef119b: jmpq 0x00007fea24ef0ff9
0x00007fea24ef11a0: mov %rdx,%rdx
0x00007fea24ef11a3: callq 0x00007fea24edda60 ; OopMap{[88]=Oop off=584}
;*new ; - com.vs.soutils.Test::<init>@5 (line 5)
; {runtime_call}
0x00007fea24ef11a8: jmpq 0x00007fea24ef103b
0x00007fea24ef11ad: mov %rdx,0x8(%rsp)
0x00007fea24ef11b2: movq $0xffffffffffffffff,(%rsp)
0x00007fea24ef11ba: callq 0x00007fea24ee1d20 ; OopMap{[88]=Oop rax=Oop off=607}
;*synchronization entry
; - com.vs.soutils.Test::<init>@-1 (line 3)
; - com.vs.soutils.Test::<init>@9 (line 5)
; {runtime_call}
0x00007fea24ef11bf: jmpq 0x00007fea24ef107c
0x00007fea24ef11c4: mov %rdx,0x8(%rsp)
0x00007fea24ef11c9: movq $0xffffffffffffffff,(%rsp)
0x00007fea24ef11d1: callq 0x00007fea24ee1d20 ; OopMap{[88]=Oop rax=Oop off=630}
;*synchronization entry
; - java.lang.Object::<init>@-1 (line 37)
; - com.vs.soutils.Test::<init>@1 (line 3)
; - com.vs.soutils.Test::<init>@9 (line 5)
; {runtime_call}
0x00007fea24ef11d6: jmpq 0x00007fea24ef10bd
0x00007fea24ef11db: mov %rdx,%rdx
0x00007fea24ef11de: callq 0x00007fea24edda60 ; OopMap{[88]=Oop [80]=Oop off=643}
;*new ; - com.vs.soutils.Test::<init>@5 (line 5)
; - com.vs.soutils.Test::<init>@9 (line 5)
; {runtime_call}
0x00007fea24ef11e3: jmpq 0x00007fea24ef10ff
0x00007fea24ef11e8: nop
0x00007fea24ef11e9: nop
0x00007fea24ef11ea: mov 0x288(%r15),%rax
0x00007fea24ef11f1: mov $0x0,%r10
0x00007fea24ef11fb: mov %r10,0x288(%r15)
0x00007fea24ef1202: mov $0x0,%r10
0x00007fea24ef120c: mov %r10,0x290(%r15)
0x00007fea24ef1213: add $0x70,%rsp
0x00007fea24ef1217: pop %rbp
0x00007fea24ef1218: jmpq 0x00007fea24edcce0 ; {runtime_call}
0x00007fea24ef121d: hlt
我们看到一遍又一遍地调用构造函数。这解释了堆栈溢出，并且似乎是递归的。
答案 1 :(得分：0)
这是递归调用，如下所述
new Test(); 以下示例显示实例变量初始化在默认构造函数调用之前运行。
public class Test {
private A a = new A();
public Test() {
System.out.println("Default constructor called");
}
public static void main(String[] args) {
new Test();
}
class A {
A() {
System.out.println("A's Constructor called");
}
}
}
输出：
A's Constructor called Default constructor called
答案 2 :(得分：0)
是的。您在无限循环中创建对象，最终得到StackOverflow
答案 3 :(得分：0)
“递归是一种可以在Java中使用的基本编程技术，其中一个方法调用自身来解决一些问题。使用这种技术的方法是递归的。许多编程问题只能通过递归来解决，还有一些问题可以解决。其他技术可以通过递归更好地解决。“ - link
dictionary.reference.com - “通过重复应用算法来定义函数或计算数字的过程。” - link
根据递归的这个定义，这不是递归。原因是你没有调用自身的方法，在这种情况下全局对象被自动实例化，因为它在全局范围内，并且该对象在其实例化的全局范围内有一个对象......
如果你注意到这个定义也提到了“解决问题”，在这种情况下，你没有解决问题。
dictionary.reference.com定义说“重复应用算法”（即方法）所以它也暗示这不是递归。
你的情况一个方法不是自己调用每次创建一个新实例即。一个新的默认构造函数，它是一个不同的方法，它不属于一个单独的对象/实例。