71 lines
1.7 KiB
Markdown
71 lines
1.7 KiB
Markdown
Java 中的 Map List String Object 判空
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## 1.Map
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可使用工具包有 `CollectionUtils` `MapUtils`
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### 返回一个空的`Map`
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```java
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// 输出1
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public static void main(String[] args) {
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HashMap<String, String> stringStringHashMap = new HashMap<>();
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boolean empty = MapUtils.isEmpty(stringStringHashMap);
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System.out.println(empty ? "1" : "0");
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}
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```
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对于`Map`其中的数值为空则需要具体判断
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```java
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// 输出0
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public static void main(String[] args) {
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HashMap<String, String> stringStringHashMap = new HashMap<>();
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stringStringHashMap.put("str",null);
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boolean empty = MapUtils.isEmpty(stringStringHashMap);
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System.out.println(empty ? "1" : "0");
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}
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```
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```java
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// 输出0
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public static void main(String[] args) {
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HashMap<String, String> stringStringHashMap = new HashMap<>();
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stringStringHashMap.put("str", null);
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boolean empty = MapUtils.isEmpty(stringStringHashMap);
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String str = stringStringHashMap.get("str");
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if (!empty && str != null) {
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System.out.println("0");
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} else {
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System.out.println("1");
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}
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}
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```
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```java
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// 输出1
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public static void main(String[] args) {
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HashMap<String, String> stringStringHashMap = new HashMap<>();
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stringStringHashMap.put("st","");
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boolean empty = MapUtils.isEmpty(stringStringHashMap);
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String str = stringStringHashMap.get("str");
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if (!empty && str != null) {
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System.out.println("0");
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} else {
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System.out.println("1");
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}
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}
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```
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### 返回一个`Map`为空
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```java
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// 报空指针
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public static void main(String[] args) {
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HashMap<String, String> stringStringHashMap= null;
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boolean empty = CollectionUtils.isEmpty(stringStringHashMap);
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System.out.println(empty ? "1" : "0");
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}
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```
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