How to attach JDK java source code to Eclipse?

If you try to see the code for JDK classes you might get this error:
Source not found. The JAR file …\rt.jar has no source attachment.

To fix this you need to attach the JDK to your IDE.

In Eclipse, select Windows -> Preferences -> Java -> Installed JREs , select the installed JDK, expands rt.jar, select “Source attachment” and find the from your disk drive, which is under the folder your JDK is installed.



Java code to find index of longest repeated letters in a string

Here’s the Java code to find index of the longest consecutive sequence of repeated letters in a string. If there is more than one run with the same length, the index of the first one is returned.
For example, if the string is(“bbbccffffiiiffff”), the program should return 5 as the longest sequence is ffff and it first appears on index 5.

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Java code to determine the validity of a binary search tree

Write a code to determine the validity of a binary search tree (BST). A binary search tree is rooted binary tree, whose internal nodes each store a key and each have two distinguished sub-trees, commonly denoted left and right. The key in each node must be greater than all keys stored in the left sub-tree, and smaller than all keys in right sub-tree. Below is an example of a BST:


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Mockito: How to mock a methods to get a parameter and return a specific value every time it’s called?

[cc lang=java]
PortBuildNumberGenerator mockBuildNumberGenerator = mock(PortBuildNumberGenerator.class);
when(mockBuildNumberGenerator.generateNextPortBuildNumberInSequence(anyString())).thenAnswer(new Answer() {

public String answer(InvocationOnMock invocation) throws Throwable {
Object[] args = invocation.getArguments();
return Integer.toString(Integer.parseInt((String)args[0]) + 1);