2.2 常用方法-Java语言基础9-常用API和常见算法

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### 拼接：
```
 public StringBuilder append(StringBuffer sb){}
 
 public StringBuilder append(CharSequence s) {}
 
 public StringBuilder append(CharSequence s, int start, int end) {}
 
 public StringBuilder append(char[] str){}
 
 public StringBuilder append(char c) {}
 
 public StringBuilder append(int i) {}
 
 public StringBuilder append(long lng) {}
 
 public StringBuilder append(float f){}
 
 public StringBuilder append(double d){}
 
```

### 在index位置插入：
 
```
public StringBuilder insert(int index, char[] str, int offset,
                                int len){}

public StringBuilder insert(int offset, Object obj){}

public StringBuilder insert(int offset, String str) {}

public StringBuilder insert(int offset, char[] str){}

public StringBuilder insert(int dstOffset, CharSequence s) {}

public StringBuilder insert(int dstOffset, CharSequence s,
                                int start, int end){}

public StringBuilder insert(int offset, boolean b) {}

public StringBuilder insert(int offset, char c){}

public StringBuilder insert(int offset, int i){}

public StringBuilder insert(int offset, long l){}

public StringBuilder insert(int offset, float f){}

public StringBuilder insert(int offset, double d) {}
 
```

### 删除 [start,end) 之间的字符：
```
public StringBuilder delete(int start, int end){}
```
### 删除 index 位置字符：
```
public StringBuilder deleteCharAt(int index) {}
```
### 替换 index 位置字符：
```
public void setCharAt(int index, char ch) {}
```
### 反转：
```
public StringBuilder reverse(){}
```
### 设置当前字符序列的长度为 newLength ：
```
public void setLength(int newLength){}
```
### 替换 [start,end) 范围的字符序列为 str ：
```
public StringBuilder replace(int start, int end, String str){}
```
### 查找字符串在字符序列中的位置：
```
public int indexOf(String str){}

public int indexOf(String str, int fromIndex){}

public int lastIndexOf(String str){}

public int lastIndexOf(String str, int fromIndex){}
```
### 截取子串：
```
public String substring(int start){}

public String substring(int start, int end){}
```
### 返回此序列中的数据的字符串表示形式：
```
public String toString(){}
```
示例：
```
package com.github.stringbuilder.demo1;

/**
 * @author maxiaoke.com
 * @version 1.0
 * 
 */
public class Test {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("helloworld");
        sb.setLength(30);
        System.out.println("sb = " + sb); // sb = helloworld                    
    }
}
```
示例：
```
package com.github.stringbuilder.demo2;

/**
 * @author maxiaoke.com
 * @version 1.0
 * 
 */
public class Test {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("helloworld");
        sb.reverse();
        System.out.println("sb = " + sb); // sb = dlrowolleh
    }
}
```
示例：
```
package com.github.stringbuilder.demo3;

/**
 * @author maxiaoke.com
 * @version 1.0
 * 
 */
public class Test {
    public static void main(String[] args) {
        StringBuilder s = new StringBuilder("helloworld");
        s.delete(1, 3);
        s.deleteCharAt(4);
        System.out.println(s); // hlowrld
    }
}
```

示例：
```
package com.github.stringbuilder.demo4;

/**
 * @author maxiaoke.com
 * @version 1.0
 * 
 */
public class Test {
    public static void main(String[] args) {
        StringBuilder s = new StringBuilder("helloworld");
        s.insert(5, "java");
        s.insert(5, "maxiaoke.com");
        System.out.println(s);
    }
}
```

示例：
```
package com.github.stringbuilder.demo5;

/**
 * @author maxiaoke.com
 * @version 1.0
 * 
 */
public class Test {
    public static void main(String[] args) {
        StringBuilder s = new StringBuilder();
        s.append("hello").append(true).append('a').append(12).append("maxiaoke.com");
        System.out.println(s); // hellotruea12maxiaoke.com
        System.out.println(s.length()); //15
    }
}
```

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