提交 9a11c4e7 编写于 作者: M Mars Liu

for merge

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# 字节流
常见的字节流类是:
## 答案
D
## 选项
### A
InputStream
### B
FileInputStream
### C
BufferedInputStream
### D
以上都是
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# File类
下面创建文件的代码错误的是:
## 答案
B
## 选项
### A
```java
File file = new File("C:\\newfile.txt");
file.createNewFile();
```
### B
```java
File file = new File("C:\\newfile.txt");
file.mkdirs();
```
### C
以上都是
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......@@ -10,7 +10,7 @@ D
### A
```Java
```java
for (int i = 0; i < 10; i++) {
System.out.println("Hello World");
......@@ -19,7 +19,7 @@ for (int i = 0; i < 10; i++) {
### B
```Java
```java
String[] arr = new String[] {"1", "2", "3"};
for (String str : arr) {
......@@ -29,7 +29,7 @@ for (String str : arr) {
### C
```Java
```java
Map<String, String> map = new HashMap<>();
for (String str : map.keySet()) {
......
......@@ -2,6 +2,6 @@
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"keywords": [],
"children": [],
"export": [],
"export": ["treeset.json"],
"title": "树集"
}
\ No newline at end of file
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# TreeSet
对于TreeSet描述错误的是:
## 答案
B
## 选项
### A
是一个有序的集合,它的作用是提供有序的Set集合
### B
它不能被克隆,因为它没有实现Cloneable接口
### C
继承于AbstractSet抽象类
### D
以上都不是
......@@ -55,6 +55,6 @@
}
}
],
"export": [],
"export": ["map.json"],
"title": "映射"
}
\ No newline at end of file
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# Map
循环遍历Map的方法正确的是:
## 答案
D
## 选项
### A
```java
for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
System.out.println("key = " + entry.getKey() + ", value = " + entry.getValue());
}
```
### B
```java
map.forEach((key, value) -> {
System.out.println(key + ":" + value);
});
```
### C
```java
Iterator<Map.Entry<Integer, Integer>> it = map.entrySet().iterator();
while (it.hasNext()) {
Map.Entry<Integer, Integer> entry = it.next();
System.out.println("key = " + entry.getKey() + ", value = " + entry.getValue());
}
```
### D
以上都是
......@@ -10,7 +10,7 @@ B
### A
```Java
```java
String a = "1";
String b = "2";
......@@ -19,7 +19,7 @@ System.out.println(a.equals(b));
### B
```Java
```java
int a = 1;
int b = 2;
......@@ -28,7 +28,7 @@ System.out.println(a.equals(b));
### C
```Java
```java
Object a = new Object();
Object b = new Object();
......
......@@ -10,7 +10,7 @@ A
### A
```Java
```java
public void test() {
Properties properties = System.getProperties();
......@@ -20,7 +20,7 @@ public void test() {
### B
```Java
```java
public void test() {
Properties properties = new Properties();
......@@ -30,7 +30,7 @@ public void test() {
### C
```Java
```java
public void test() {
Properties properties = new Properties();
......
......@@ -10,7 +10,7 @@ D
### A
```Java
```java
List<String> array = new ArrayList<String>();
Iterator<String> it = array.iterator();
......@@ -23,7 +23,7 @@ Iterator<String> it = array.iterator();
### B
```Java
```java
for (int i = 0; i < array.size(); i++) {
String s = array.get(i);
......@@ -33,7 +33,7 @@ for (int i = 0; i < array.size(); i++) {
### C
```Java
```java
for (String str : array) {
System.out.println(str);
......
......@@ -10,21 +10,21 @@ C
### A
```Java
```java
HashSet
```
### B
```Java
```java
TreeSet
```
### C
```Java
```java
LinkedSet
```
......
......@@ -10,21 +10,21 @@ D
### A
```Java
```java
HashMap是有序的
```
### B
```Java
```java
Hashtable不是线程安全的
```
### C
```Java
```java
ConcurrentHashMap无法保证并发的安全性
```
......
......@@ -10,7 +10,7 @@ A
### A
```Java
```java
Random random = new Random();
int result = random.nextInt(10);
......@@ -19,7 +19,7 @@ result = result + 1;
### B
```Java
```java
Random random = new Random();
int result = random.nextInt(1);
......@@ -28,7 +28,7 @@ result = result + 10;
### C
```Java
```java
int max = 10;
int min = 1;
......
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# 算术运算符
执行完下面的代码,变量b的值是:
```java
int a = 1;
int b = a++;
```
## 答案
A
## 选项
### A
1
### B
2
### C
3
### D
以上都不是
......@@ -11,6 +11,6 @@
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\ No newline at end of file
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\ No newline at end of file
# 自动递增和递减
下面代码执行后的结果是:
```java
int a = 0;
a = ++a;
int b = 0;
b = b++;
System.out.println("a = " + a);
System.out.println("b = " + b);
```
## 答案
A
## 选项
### A
a = 1
b = 0
### B
a = 1
b = 1
### C
a = 0
b = 1
### D
以上都不是
......@@ -2,6 +2,6 @@
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......@@ -11,6 +11,6 @@
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# 关系操作符
下面代码执行后的结果是:
```java
Integer n1 = new Integer(47);
Integer n2 = new Integer(47);
System.out.println(n1 == n2);
System.out.println(n1 != n2);
```
## 答案
B
## 选项
### A
false
false
### B
false
true
### C
true
true
### D
以上都不是
......@@ -11,6 +11,6 @@
}
}
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"export": ["logic.json"],
"title": "逻辑操作符"
}
\ No newline at end of file
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# 逻辑操作符
下面的语句能够打印出 `CSDN`的是:
## 答案
B
## 选项
### A
```java
boolean flag1 = true;
boolean flag2 = false;
if (!flag1 || flag2) {
System.out.println("CSDN");
} else {
System.out.println("Java");
}
```
### B
```java
boolean flag1 = false;
boolean flag2 = false;
if (flag1 && flag2) {
System.out.println("1024");
} else {
System.out.println("CSDN");
}
```
### C
```java
boolean flag1 = true;
boolean flag2 = false;
if (flag1 && flag2) {
System.out.println("CSDN");
} else {
System.out.println("NDSC");
}
```
### D
以上都不是
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# 按位操作符
下面代码执行后的结果是:
```java
System.out.println(1 & 2);
System.out.println(1 | 2);
```
## 答案
D
## 选项
### A
0
1
### B
1
3
### C
2
2
### D
以上都不是
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# 移位操作符
下面代码执行后的结果是:
```java
int a = 2, b = 2;
System.out.println(a << b);
int c = 2, d = 2;
System.out.println(c >> d);
```
## 答案
A
## 选项
### A
8
0
### B
16
-1
### C
2
2
### D
以上都不是
......@@ -2,6 +2,6 @@
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# 三元操作符
下面代码执行后的结果是:
```java
int a = 10;
int b = 20;
System.out.println(a == b ? 0 : 1);
```
## 答案
B
## 选项
### A
10
### B
1
### C
20
### D
以上都不是
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# 字符串操作符
下面代码执行后的结果是:
```java
String s1 = "1";
int s2 = 2;
System.out.println(s1 + s2);
```
## 答案
C
## 选项
### A
3
### B
1
### C
12
### D
以上都不是
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